Apple (NASDAQ:AAPL) just turned in the best earnings report in history. At $18 billion, Apple's quarterly profit was more than any other company has ever earned. Revenue rose 30%, earnings jumped 48%, andApple's cash hoard is now sitting just shy of $180 billion.

Indeed, the company appears to be firing on all cylinders, and consumers are eagerly snatching up its high-priced, high-margin iPhones.

But while it's hard to say anything negative about Apple's earnings report, in the interest of skepticism, there are still a few factors that should concern shareholders.

1. Apple's business is now almost entirely dependent on the iPhone
Apple's business is, for all practical purposes, the iPhone. Last quarter, iPhone sales generated roughly 69% of Apple's revenue, up from about 56% in the same quarter last year. Apple's services -- iTunes, Apple Pay, Apple Care -- accounted for 6%. Given that the bulk of these services are directly related to the iPhone, Apple's handset now accounts for nearly three-quarters of its revenue.

Clearly, Apple's iPhone is a tremendous product, and the iPhone 6 and iPhone 6 Plus, in particular, have been amazingly successful. But to be so overwhelmingly dependent on one product alone could make Apple vulnerable to changing conditions in the handset market.

Its chief rival, Samsung, has seen its shares drop and its earnings plummet after competition from Apple and other vendors reduced the demand for its Galaxy handsets. Yet, Samsung still has a number of other business units to fall back on -- including semiconductors, memory chips, televisions, and appliances, among others. Apple doesn't have the same luxury, and if the iPhone ever falls out of favor, Apple could struggle.

2. Demand for the iPad continues to fall
Apple's increasing dependence on its iPhone is mostly due to its growing popularity -- Apple sold 74.5 million handsets last quarter, a new record. But almost equally as important is the decline of iPad. Sales of Apple's tablet fell 18% on an annual basis, continuing a trend that has been ongoing for more than a year. The iPads Apple sold were also cheaper, leading to 22% drop revenue.

Apple's management continues to argue that the iPad has a bright future in the long-run, and that it should benefit from Apple's push into the enterprise. That may be true, but at this point, the once popular notion that its iPad would eventually emerge as Apple's most popular product seems quite unrealistic.

3. China is quickly becoming Apple's most important market
Last, and frankly least concerning, is Apple's increasing reliance on China. Moving into China has actually been one of Apple's stated goals, and the increasing amount of revenue it derives from the country is more of a reason to cheer than to be alarmed, but the Chinese market poses a number of unique risks.

China's policies on intellectual property are famously lax. The familiar designs utilized by its Chinese rival Xiaomi, for example, are tolerated in China, but unlikely to fly elsewhere. Apple's reliance on hardware sales makes it less likely to suffer from piracy -- an issue that has long plagued competitors like Microsoft in China -- but the Chinese government has been more vocal in its desire to see homegrown companies dominate the mobile space.

In May, 2013, a Chinese government research institution specifically called out the Android operating system for being too dominant in China. Ultimately, nothing of substance came from the report, but it did highlight a risk -- if Apple becomes too dominant in China, the Chinese government could actively work to undermine it.

While this risk is minor, it's one still worth considering. China is now the iPhone's second-largest market, and Apple's third largest overall (behind Europe by only 1%).