Apple's (NASDAQ:AAPL) been on a roll as of late. Boasting a 1-year return of nearly 40% and approaching its all-time high for market capitalization -- approximately $650 billion -- it's no wonder that fans are increasingly excited about the company again.

For perspective, Apple reached its high-water mark before the release of its iPhone 5 in September 2012 and fell after reporting selling "only" 5 million units over the launch weekend. The decline continued into 2013 and dragged the company below $400 billion. And now we're approaching those crossroads again--Apple is nearing all-time highs right before a major iPhone iteration release. The question for investors is if this time be different.

A comparison
As investors, ultimately you are paying for earnings. So it is entirely appropriate to compare Apple's income statement before the iPhone 5 release to its current performance.

PeriodTTM RevenuePrior PeriodPercentage ChangeTTM EPSPrior PeriodPercentage Change
Pre-iPhone 5 $148.8 $100.3 49.7% $6.15 $3.66 68%
Pre-iPhone 6 $178.1 $169.4 $5.1% $6.23 $5.76 8.2%

Source: Apple's 10-Q's. Revenue figures in billions. EPS are split adjusted

As you can see, growth in both revenue and earnings per share has slowed. The pre-iPhone 5 Apple had grown its top line an amazing 50% on a year-over-year basis. That's hard for any company, especially one that reported a trailing-12-month revenue figure of over $100 billion. In addition, Apple exhibited economies of scale by growing EPS more than its revenue by clocking in at 68% growth.

Of course, it would be nearly impossible for Apple to continue to grow at such a rapid clip as the company became larger, but you can see how growth has slowed before the iPhone 6 release. On the same trailing-12 month comparison, Apple reported $178.1 billion in revenue -- good for 5.1% growth from the corresponding period.

That's solid, but not flashy growth. On a more positive note, the company was able to turn that into an earnings-per-share growth of 8.2%, in part due to its massive share buyback program. But it's safe to say that today's Apple isn't as high-growth as it once was.

Apple's increasing reliance on iPhones
Compounding things a bit is Apple's reliance on iPhone sales. As the chart below shows, since the fourth quarter of 2012 more than 50% of Apple's revenue has come from one product:

Source: Apple's 10Qs

This is both a blessing and a curse for Apple investors. On the plus side, it is widely reported that Apple's iPhone is its highest-margin product. So the positives are as a larger percentage of revenue is iPhone sales, less is spent on cost of goods sold and should fall down the income statement to earnings per share.

The negative is that an over-reliance on one product makes the company a riskier investment. See, much like diversification lowers risk for your individual portfolio, product diversification lowers risk for companies. As Apple continues to derive over half its revenue from one product, investors should keep an eye on both competition and smartphone demand.

With that being said, one key area Apple investors should watch as far as iPhone sales go is China. Apple's rumored new phone is approaching phablet size which is a very popular form factor in Asia. In addition, Apple has secured agreements with all major China telecoms -- including China Mobile -- for them to carry Apple's iPhone.

Well, should I buy the stock before the launch?
Here at The Motley Fool we're long-term investors and typically eschew "momentum trades," therefore I encourage you to do that same. For those investors that are evaluating Apple as a long term investment, I'd look beyond the iPhone 6.

Specifically, what new ideas and plans does Cupertino, California have to keep that top line growing. Rumors persist about a new payment service or a smartwatch. If Apple wants to keep its top line growing, a new product or service is what potential investors should keep their eye on, not the newest iteration of its iPhone line.