Simply put; what does my $99 get me, that I can't already get for free?
OK, OK, sounds like a dumb question, but the Apple site is not clear to me.
My hunch is that you get the ability to submit apps to the app store for your 99, but you could get everything else for free, but it's not clear to me hence the question.
After paying the $99 the main benefits are shown below:
Those are the main benefits, I don't think I have forgotten any of the key benefits.
For $99 you can run your app on your actual device and you can sell your app.
You cannot actually run your program on a any iPhone/iPod touch, including the one you own, without paying the $99.