It's not just the cost. It's also the bureaucracy and loss of control that the App Store creates. Releasing and maintaining an app as an individual developer is difficult enough without adding a whole layer of unnecessary red tape and fees that serve no legitimate purpose.
Why not? If you have a half decent app and it helps people, and that gives you some satisfaction, do it. That's a well spent $99. Everyone already spends more money on less worthy things.
