If this model of selling software is so successful for the iPhone why don't they have an app store for the Mac? I mean maybe if more desktop applications cost 99 cents they'd be selling more of them.
The price point isn't the core of the success of these apps, it's the distribution. Imagine for a moment that when you searched "mac applications" on the internet, only ONE website came up. Imagine as well that this ONE website gave away free front page advertising to apps with the highest volume.
In that scenario, your only source of new users for your app is the ONE webste, and the best way to get positioning is to maximize volume. Thus you price your app for volume and you target your audience for volume.
Also there's no built in payment system for the web. It'd actually make sense for ISPs to launch a payment model, whereby you go to some website, agree to pay X for something, and it just gets added to your ADSL/phone bill.
Then we might see some really cool premium models around on the web.
"In that scenario, your only source of new users for your app is the ONE webste [sic]..."
And that, right there, explains why I won't go anywhere near the App Store, or support the Apple/iTunes/iPhone dev ecosystem with my time or code. There might be money to be made, but only as long as Apple likes you and allows you to continue to play in their sandbox.
Would anyone be that surprised if iTunes suddenly started distributing Mac software? I wouldn't bat an eye if the latest iLife and iWork suites and Final Cut Express suddenly showed up there, for instance.
Its an excellent question. Aside from the points already mentioned, the app store for the iPhone conveniently hooks into the payment scheme you have for the phone. No need to fool around with credit card numbers, trust issues, etc. (Basing this on the iTunes store would be a good idea with many of the same advantages.)