What about the exposure it gives you app, and (potentially) much more sales (it has hundreds of millions of users with credit card, and buying stuff is just one click)?
I've sold so many items that would otherwise live forever in a closet because they'd be too hard to find a local buyer. The number of eyeballs looking at eBay makes the place a huge net win.
But, App Store is a very good thing for developers. You can make a Chess game both with ObjC and HTML5, but chances of someone finding your HTML5 app via Google (search) is practically zero. On the other hand, because there are less than 150 Chess games for iPhone, if a random surfer searches the App Store for 'chess', they see your icon down the list. That's the exposure I'm talking about.
And again, I don't like Apple's rules very much, I'm just stating that being on the App Store brings you a lot of exposure.