Apple's differentiator has been quality for a long time; beautiful industrial design coupled with an elegant user experience. Independent developers building Mac OS X apps know how high Apple's standards are because to build a really great app for the Mac it should act and feel as if Apple made it. Some developers go above and beyond the HIG and produce beautiful, custom UIs that surpass what Apple might have built if they developed the same app. If you're working at this caliber then perhaps you're gunning for an Apple Design Award or have already won one.
When the iPhone App Store first launched, many of the first available apps were written by established, well-known Mac developers who were well aware of Apple's standards for quality. Few people had experience with Objective-C and Cocoa outside the Mac developer community so it was a given that Mac developers would be out in front, leading the way.
Now that the App Store is hugely profitable most iPhone apps are developed by newly-minted iPhone developers, not hardened Mac folks like when the App Store debuted. These developers are coming from dozens of other platforms to try and strike gold on the iPhone. This may be the first time they've heard of Cocoa or even used a Mac. If you haven't been using a Mac for awhile then you're bound to not really understand what makes an app "Mac-like." Here's a quote from John Gruber:
"Anyone involved in Mac software development is familiar with arguments over whether a particular app is "Mac-like". In the early days of the Mac -- the first decade or so -- the entire Mac community was largely in agreement about just what this meant. To be un-Mac-like was to be ignorant of the fundamental concepts and norms of the Mac OS. It was something you could spot in an instant -- software designed by engineers who just did not get it."
If you love the iPhone platform and want to build an app that feels "iPhone-like" then using Xcode and standard UIKit interface elements is a simple way to start. You'll subscribe to some iPhone development blogs, buy some Cocoa Touch books, and really dive into the new platform. If you really, deeply care about the user's experience then you'll probably hire an interface designer and tell him or her that you want your iPhone app to look as if Apple could've designed it. You'll sweat every detail including every icon, every widget, every pixel, every font. You'll cherish the first time you use your finished app.
If you're building an iPhone app because the iPhone is the hot platform and you're interested in cashing in then you might take a different path. You might be coming from another platform and another language and want to get started right away. You might not want to spend the effort and time to learn Objective-C, you'll probably want to utilize the skills you already have. Hell, you might not even own a Mac or even particularly like the iPhone. You'll probably search for ways to start building iPhone apps without using Objective-C and find some interesting "meta-platforms" that you can use. You care about the user's experience insofar as the user can access the features of your app without much trouble. You're not interested in fancy animations and other things you think are just window dressing, you just want your app to work. You'll cherish the first time you sell a copy of your app.
Using Xcode and Objective-C are not surefire ways to build decent iPhone apps, and using "meta-platforms" and other languages are not surefire ways to build crappy, non-Apple-like iPhone apps. Are they indicators about how much passion someone has for the iPhone platform and building quality iPhone user experiences? In my experience the answer is yes.
Steve Jobs wants Apple to be the arbiter of quality in the App Store, denying apps that are ugly, poorly-thought, lame, explicit or featureless. He can't say that in the Terms and Conditions so instead they're using carefully-worded language that excludes certain technologies associated with the kinds of apps he doesn't like. Steve Jobs doesn't want shit in his App Store. If you're a developer who may be interested in building shit, there's another platform right down the street.
Speaking from the point of view of someone who wants to build beautiful, high-quality apps for the iPhone and iPad: if you're too lazy to learn how to build iPhone-like iPhone apps using Apple-supplied tools then get the hell out of my App Store, too.