I think a lot of it has to do with that 30% cut. 30% of a $25 app isn't that much, but I guess if I were someone big like Autodesk or Adobe and it were my big, multi-thousand dollar app, why would I want to give Apple a 30% cut when the distribution model that I have now works already? I guess that's why you see a lot of 'Lite' or 'Debut' edition apps, something to entice you over to the more expensive apps which can then be purchased without Apple taking a cut. There's no real benefit (and lots of downsides) as a developer if you don't need the Mac App Store for the exposure.