Not Enough Developer Support!
But wait, there is already a large community of web developers out there, why don't they code for the webOS? Simple, there are so many frameworks, tool sets out there in that land that for any given technology, only a small fraction of people actually know it well enough to do the really cool stuff. Most are probable of the cut and paste type of programmers.
One more thing, were we not their years ago with BeOS, vastly superior to anything out there at the time, but failed to gain market acceptance due to lack of developer support (M$ anti competitive behavior didn't help matter either). I always said that if the just made a solid Java API and pushed that, then it might actually have gained some traction.