Less than two years ago, Apple's (NASDAQ:AAPL) iPad absolutely dominated the tablet space. As of mid-2012, Apple still claimed nearly 70% of the tablet market, while Android tablet manufacturers were struggling to make any headway.

Furthermore, the iPad Mini's fall 2012 arrival was an open secret by then. As a result, tablet market analysts expected Apple to further solidify its dominance of the tablet market over time.

The iPad Mini was supposed to solidify Apple's dominance in the tablet market. (Photo: Apple.)

However, the opposite has occurred. Not only has Apple's market share lead crumbled, but iPad sales growth has also come to a crashing halt. Tablet rivals such as Amazon.com (NASDAQ:AMZN) and Samsung are gaining momentum by closing the quality gap with Apple and offering lower price points. Unless Apple can deliver vastly improved iPads later this year, the iPad's growth days are over.

Where did all the iPad buyers go?
It's hard to imagine right now, but just two years ago, Apple was growing iPad revenue by more than 60% and iPad unit sales by 80% -- even without an entry in the growing 7- and 8-inch tablet market! Last year, despite the addition of the iPad Mini, unit sales growth slowed to 22%.

Furthermore, Apple introduced the iPad Mini at a lower price point to combat cheap tablets from Amazon.com and other vendors. This led to a sharp drop in the average iPad selling price. As a result, iPad revenue grew only 3% in FY13. While iPad production costs are falling, it's safe to say that with iPad unit sales growth outpacing revenue growth 22% to 3%, iPad margins dropped dramatically.

iPad revenue growth did tick up to 7% last fall on a 14% increase in unit sales. However, that may prove to be Apple's best quarter of the new fiscal year. Demand appears to have fallen off a cliff after the holiday season.

The iPad Air got off to a fast start -- but demand has been cooling off. (Photo: Apple.)

As of Dec. 28 -- the last day of Apple's fiscal Q1 -- the iPad Air and iPad Mini Retina combined to account for 8.6% of all iPad usage, according to Fiksu. By the last day of Q2, usage for the new iPads had grown to 14.1% of the total, a 5.5 percentage point increase.

Considering that Apple benefited from "channel fill" in Q1 -- selling the new iPads to build up inventory at third-party retailers -- iPad unit sales could easily have fallen 40% sequentially this quarter. That would entail a significant step backward from Apple's 19.5 million iPad sales in Q2 last year, when Apple was meeting pent-up demand for the original iPad Mini.

The iPad Mini Retina is a flop
If I had to boil down Apple's iPad problems to a single issue, it's that the new iPad Mini Retina is a flop. After five months on the market, the iPad Mini Retina accounts for just 3.7% of all iPad usage (as of Thursday). By contrast, the third-generation iPad (the first to offer a Retina display) still accounts for 13.6% of iPad usage, even though it was on the market for less than eight months in 2012.

iPad Mini Retina sales have fallen way short of expectations. (Photo: Apple.)

To some extent, weak sales of the iPad Mini Retina could be the result of a crowded iPad market. For just $100 more, tablet buyers can get a whole lot of extra screen real estate with the iPad Air. Alternatively, the original iPad Mini is $100 cheaper and offers "good enough" specs for many users.

However, there's also a quality issue. To be sure, the iPad Mini Retina has gotten good reviews from some respected publications. That said, many reviewers have found that Amazon's Kindle Fire HDX offers a much higher-quality display than the iPad Mini Retina.

Reviewers have raved about the displays on Amazon's Kindle Fire HDX tablets. (Photo: Amazon.com.)

This is a big problem for Apple, which spent most of 2012 training consumers to demand high-quality Retina displays for their mobile devices. Not only is Amazon offering lower price points -- the Kindle Fire HDX starts at $229 for the 7-inch version and $379 for the 8.9-inch version -- but it's also offering better quality on at least one critical feature.

Will Apple reclaim the lead?
In some respects, Apple's commanding lead in the tablet market remains intact. There are far more iPad-optimized apps than tablet-optimized Android apps. Even though Apple's technical lead has shrunk (or disappeared, perhaps), it still offers a superior overall user experience. That's a major reason iPad usage still dwarfs usage of all other tablets combined.

The iPad can still be a meaningful contributor to Apple's profitability even if sales growth remains small. As long as engagement remains high and the installed base of iPads increases, Apple can take a page out of Amazon.com's playbook by making money while people use their iPads: by selling apps, books, movies, and so on.

Indeed, strong iPad usage is undoubtedly one of the factors driving big gains in Apple's revenue from iTunes and the App Store. This revenue stream will become increasingly important to Apple's earnings in the next few years. However, what Apple shareholders really want to see is a return to solid sales growth for the iPad -- even if it continues losing market share.

Apple needs to double down on display quality if it wants to reignite iPad sales growth.

To reignite iPad sales growth, Apple may need to become somewhat more aggressive on pricing for the iPad Mini Retina. More importantly, it needs to make the display at least as good as what Amazon and other competitors are offering (and preferably better). Adding a faster processor and a fingerprint sensor may help sales a bit, but improving the display is the X-factor.

Foolish final thoughts
While I remain bullish about Apple's long-term prospects, the iPad no longer appears to be a major part of the Apple growth story -- aside from its role in driving content and app sales. iPad sales have stagnated in the last year, and the introduction of two new iPads last fall provided only a modest short-term sales bump.

To reverse this discouraging trend, Apple needs to double down on its pursuit of perfection for the next iPad Mini. If Apple can deliver an updated iPad Mini Retina with a best-in-class display this fall, it could rejuvenate iPad sales, especially if Apple can lower the price. Otherwise, investors may need to look to other product lines for long-term growth.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.