In the eight years since the iPhone first launched, the device has made up an increasing share of Apple(AAPL 2.86%) revenue. In the last 12 months, the iPhone accounted for about 64% of the top line. Some critics point to this as a huge risk facing Apple shareholders, and indeed, a complete flop could put a big dent in its market value.

But Apple completely dominates the smartphone market and should continue to do so for the foreseeable future. Here are five charts to show you why.

Increasing share of smartphone profits
Apple might not sell the most smartphones in the world -- that title still belongs to Samsung -- but it generates more than 10 times the profit Samsung makes on its smartphone sales as of the fourth quarter of 2014. Combined, both companies account for essentially all of the operating profits in the smartphone industry.

Source: Canaccord Genuity. Chart compiled by author

Apple and its closest competitor, Samsung, have moved in opposite directions regarding industry profit share since the third quarter of 2013, when both companies had shares in the mid-50% range. Samsung has felt the pressure from low-end and mid-range device manufacturers, while Apple has stuck to its premium-only business model while managing to continue increasing unit sales.

China loves the big screen iPhones
Many investors are worried about the growing presence of China in the smartphone market. Indeed, the country has grown into the largest smartphone market in the world, and many associate the country with low-end entry-level phones.

Source: IDC. Chart compiled by author

However, with the release of the new larger screen iPhone models last fall, China saw a sudden surge in the average selling price. Demand for the new iPhone 6 and iPhone 6 Plus in China lifted the average selling price for a smartphone in the country by more than $40 per unit.

Brand loyalty remains high
One reason Apple has been able to increase sales even as more competition comes to market is its strong brand loyalty. When a consumer decides to purchase an iPhone, it is unlikely to be his last iPhone purchase. A recent survey from RBC Capital found that 83% of iPhone owners plan to buy another device versus just 64% for Samsung.

Source: RBC Captial. Chart compiled by author

Note that almost 10% of Samsung owners plan to switch to an iPhone for their next smartphone, versus just over 4% for Apple owners switching to Samsung. That means the profit share gap between the two companies will only continue to increase.

Purchase intent
Apple currently holds a 43.5% share of the U.S. smartphone market, according to ComScore. That same RBC survey found that 43.3% of U.S. consumers plan to buy an iPhone as their next smartphone.

Source: RBC Capital. Chart compiled by author

While that might sound like Apple's share of the market is stalling after increasing from a 15% share in 2012, look at how many people are still undecided. If Apple captures just 20% of the undecided crowd, its share of the U.S. market could climb to 48%.

App Store revenue points to more lock-in
At Apple's Worldwide Developer Conference this year, the company announced it has paid out a cumulative $30 billion in royalties to app developers. Put another way, iPhone and iPad owners have bought over $40 billion worth of apps. That is a big investment among the 700 million to 800 million iOS device owners. Comparatively, Google Android owners have spent about one-third that amount.

Source: Google and Apple. Chart compiled by author

It is worth noting that Android app purchases are starting to catch up with Apple. However, that is with twice the user base, so the average Android owner is spending less than half the amount on apps compared to iPhone owners, making the ecosystem less sticky.

Complete dominance
Apple's dominance of the smartphone market only continues to increase. Its market share of the two biggest smartphone markets -- China and the U.S. -- is on an upward trajectory, and it is doing so without sacrificing profits. Those factors help reduce the risk of having so much revenue concentrated in the iPhone.