Speaking as a shareware developer...
A lot of developers really like the App Store because it means they don't have to pay for their own bandwidth, maintain their own ecommerce systems, host the app for download themselves, track and send out customer records, and so on, and so on.
That kind of stuff is surprisingly tedious, difficult, and expensive. Apple handles everything from hosting to bandwidth to customer records (you'd be surprised how many folks register my software and then email me six months later to say they've lost the serial number; with App Store purchases, I as a developer would not have to deal with that).
Apple charges 30% of each transaction as their cut. That might sound like a lot, but many developers I know are more than happy to pay it. If as a developer you want to go your own route, your choices are to go through PayPal (which takes a smaller cut, but is sometimes finicky and problematic), get your own credit card merchant account and payment gayeway (which is what I do--it's cheap but there are a huge number of hoops you have to jump through, and you're responsible for maintaining your ecommerce software, payment gateway, and so on, plus keeping on top of security, maintaining compliance with the PCI security requirements, keeping on top of patches and security updates for your software, and so on, and so on), or you can go with a remote-hosted shopping cart who will do that all for you...and probably charge you, err, 30% of your transactions as their fee.
If you have a popular app, the bandwidth bills can add up fast. If you want to sell through your own merchant account, you'll still pay transaction fees, plus merchant accounts are extraordinarily difficult to get for companies that have not been in business for many years. When you actually start looking at it, the Apple App Store starts to look like one hell of a good deal.
If I could distribute though the app store, I would. I continue going my own way only because my apps don't meet Apple's requirements--therein is the rub, at least for me.
A very detailed and enlightening post.
Thanks.
