I thought this was an interesting point from John Casasanta, a developer who who creates both Mac and iPhone applications:
For one, developing for the iPhone is a dream compared to developing for the Mac. Yeah, it’s Cocoa development for both iPhone and Mac, but many of the Mac SDKs are old and crufty compared to the shiny, new iPhone one. This means much quicker development time and greater programmer satisfaction. Many, many programmers I know never want to go back to Mac for this reason and usually cringe when they have to.
Oh, and there’s the attention:
Another major factor is the “rock star” one… When you create Mac apps, you have little chance of having your apps in TV ads, Apple retail store promotions, WWDC promotions, on TV networks like CNN and CNBC, etc, etc, etc.