In 2013, Apple (AAPL 0.46%) stock underperformed the S&P 500, gaining just 5% compared to the S&P 500's gain of 29% to all-time highs. Although a few major concerns worrying Apple investors were addressed during the year, several other factors continue to leave the market uncertain of whether or not Apple can continue to grow its bottom line over the long haul. Looking back, here's a look at major developments investors had an eye on for Apple stock in 2013 and updates on their current situations.

A growing cash hoard
When 2012 began, Apple had too much cash on its balance sheet. Although Apple had initiated a dividend and a small repurchase program in 2012, it wasn't significant enough to please investors. Apple faced immense pressure to take action. Hedge fund manager David Einhorn even made headlines early in the year proposing Apple pay out more of its cash. Apple followed up to Einhorn's proposal by admitting that it was "in the fortunate position of continuing to generate large amounts of cash, including $23 billion in cash flow from operations in the last quarter alone."

Fortunately, Apple did boost the amount of cash it is returning to shareholders. In April, Apple more than doubled the amount of cash it was returning. Most importantly, it boosted its share repurchase program from $10 billion to $60 billion.

New categories
Since Steve Jobs passed, Apple still hasn't entered any new product categories. In fact, the last category Apple entered was tablets in January 2010. While Apple has arguably continued to innovate in its existing product categories, in the past Apple has relied on periodically entering new product categories in order to grow over the long haul -- an undertaking that Apple CEO Tim Cook hasn't managed to accomplish yet.

The pressure is on. Even Apple's board has reportedly expressed concern over Apple's pace of innovation, according to Fox Business. This leads us to a key question: Can Cook live up to Jobs' high standards?

2014 may be the year Apple launches a product in a new category. In fact, Apple may be planning to launch products in two new categories in 2014, according to DisplaySearch: an iWatch and an Apple television.

Margins
After Apple reported its first-quarter earnings in 2012, the company's gross profit margins were a real concern. Year-over-year, they were down more than 600 basis points. Could Apple stabilize its gross profit margin? An end of the year update on Apple's gross profit margin story suggests it has.

Cheap iPhone
Given Apple's paltry market share in China, investors had hoped that Apple's rumored lower-cost iPhone would be cheap enough to combat low-cost alternatives to the iPhone in China. When Apple's iPhone 5c finally launched, the pricing was only marginally lower than its flagship 5s pricing.

iPhone 5c

Initially, this spooked the Street. But as time goes on, criticism of the not-so-cheap iPhone 5c seems to be subsiding. There are several signs that Apple made the right move with the iPhone 5c. Particularly, the 5c appears to be attracting first-time iPhone buyers in the U.S. and the iPhone 5s is doing considerably well in China. In fact, without having to compete with the aggressively priced iPhone the market had anticipated Apple would launch, the iPhone 5s may actually soon become the top selling smartphone in China, according to recent data from Counterpoint research.

China Mobile
Possibly one of the biggest hopes Apple investors had going into 2013 was that Apple would finally announce a deal with the world's largest carrier, China Mobile. It may have taken all year for Apple to do so, but it finally did in December. Unfortunately, we won't get so see the fruits of this arrangement until 2014.

Just how big of an opportunity is China Mobile for Apple? It's tough to tell. But it certainly will have a positive impact on Apple's bottom line.

What's next?
Reviewing 2013, Apple's business looks solid. Though margins have slightly contracted, an aggressive share repurchase program and an arrangement with the world's largest wireless carrier should serve as nice catalysts during 2014. Even better, the stock is priced conservatively after significantly underperforming the S&P 500 -- an uncommon scenario for market leaders in this pricey market. So, it's not too late for investors take a stake in Apple at a reasonable price.