When Apple unveiled the iPhone 4S last week, reaction from the media was generally mixed. With many anticipating the launch of the iPhone 5, many pundits quickly labeled the 4S a disappointment.

But don’t tell that to consumers. The iPhone 4S is selling like hotcakes. In the first 12 hours of taking pre-orders, AT&T had already sold 200,000 units.

By the end of the day Friday, pre-order stocks were sold out across all three carriers in the U.S. offering the iPhone, AT&T, Verizon and Sprint. The same thing reportedly happened in other countries where 4S pre-orders were being accepted.

In all likelihood, the iPhone 4S will be the fastest-selling iPhone yet. So what gives? Why did so many pundits get it so wrong? There are three primary reasons.

Apple has incredible brand loyalty

Few companies can claim the type of brand loyalty Apple has earned. Apple, for obvious reasons, can’t abuse this brand loyalty. If it starts to deliver products that disappoint consumers once it’s in their hands (as opposed to pundits who base their opinions on a keynote speech), that brand loyalty can evaporate.

Right now, consumers trust that when Apple delivers a new product, it will deliver something that’s ‘better.’ So long as Apple maintains that trust, consumers will line up to buy it’s products. It’s that simple, even if some would like to believe that there’s a more sophisticated consideration taking place.

The iPhone is a fashion accessory

The mobile phone you carry, like the clothes you wear, is a statement about who you are. Apple has done something few other companies have with the iPhone: they’ve turned it into a fashion equivalent.

Yes, the iPhone 4S looks just like the iPhone 4, but the difference between a $3,500 Louis Vuitton handbag and a $200 handbag from another designer is probably not instantly perceptible to most.

That doesn’t matter: owning the latest and greatest is something that simply feels good. As vain or superficial as it may sound, many will be proud to count themselves as one of the first iPhone 4S owners.

Apple gets incremental change right

The media, analysts and Apple fanatics expect great things from Apple. One of the expectations: that Apple will be a revolutionary force in the technology industry. But that, in my opinion, is a fairly unsophisticated understanding of Apple.

Yes, one could argue that Apple has done revolutionary things, but when it comes to product evolution, Apple is really a master of incremental change.

When you buy the latest version of an Apple product (like the iPhone), you expect that you will be able to use it just as you did the previous version. There may be new features and capabilities, but by and large, you can upgrade Apple products without being forced to relearn what you thought you knew how to do, or being thrown into a completely new paradigm.

That sounds pretty straightforward, but it’s really important. If you’ve used Microsoft products, for instance, or even a handful of Android phones, you know that ‘upgrading‘ can be a jarring if not confusing experience.

With the iPhone 4S, Apple has made significant upgrades under the hood, and added some potentially significant software features, but if past is prologue, you can bet that Apple has not made going from the iPhone 4 (or even the iPhone 3) to the iPhone 4S a rotten experience. That matters.