Though Apple (AAPL) is still up more than 40% year-to-date, shares have fallen 7% in the last five days and is actually pushing the NASDAQ (^IXIC) down for the quarter; an almost unthinkable notion over the last year. Every down-tick has turned out to be a buying opportunity over the last decade. This historic performance has given Apple investors a sense of invulnerability, and complacency is the enemy of investment returns.

But, Sean Udall, tech analyst and founder of the TechStrat Report, has four reasons he's concerned about the stock of Apple.

By way of context, Udall is not an Apple perma-bear looking for attention. In fact, he owns shares and has been pounding the table for years. What's lost on so many Apple enthusiasts is something Udall never forgets: Every party must end, it's just a matter of when.

Udall's concerns aren't about this moment, this week or even necessarily this year. In the attached video he's talking about macro headwinds Apple must overcome to keep the title of Best Company on Earth.

1. Apple is going more proprietary on Chips

Udall says Apple is increasingly given to producing the chips driving its products in-house.

While this may save them some money upfront, assuming they can create enough efficiencies, Udall says Apple going its own way will turn companies like Qualcomm (QCOM), Broadcom (BRCM), Marvell (MRVL), and Intel (INTC) into fierce competitors.

"I don't know if any one company can take on the whole silicon chip industry," he concludes.

2. Flash margins will suffer if the chip customers become competitors

"My second concern is Apple has made a ton of money reselling flash and marking up flash memory," Udall says. "There's this huge 80 - 100% mark-up game that might not last forever."

It plays back into the first problem. "If Apple cuts out more of the silicon valley industry, the chip sector, that incentivizes all these companies to make sure the competing products are that much better," he says.

3. The end of iPhone subsidies.

Starting with the original AT&T (T) deal for the first iPhone, companies have been paying Apple for the right to sell their product. Regardless of the huge ticket, the price you pay for your phone at the cellular store actually represents a negative margin proposition for the seller.

"If one of the big three Sprint (S), Verizon (VZ), or AT&T radically reduces the subsidies you almost have to reduce the product price from Apple," says Udall. "That would lead to a big margin hit."

It's not a total hypothetical. AT&T is already making noises in the direction of reduced subsidies and with reduced dominance of Apple in the smart phone category (see below) the other carriers will follow.

4. Competition

Udall hears analysts saying there's "no competition" for Apple, but he begs to differ.

Starting with smartphones, Udall notes that Google's (GOOG) "Android has gone from 3 or 4% market share to 50% market share. There's certainly competition out there."

While not yet a major concern, ultralight laptops are still looming as a competitor for iPads, as are other products and tablets. "You're going to sell a lot of iPads," he says, "but if iPad growth goes from 80 to 100% down to 20%" there's no way the stock isn't going to get hit.

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