Lucy Black over at I Programmer has a theory about why there are so few tablet apps for the "Honeycomb" version of Android:
Moreover many, both device manufacturers and app developers are waiting for the soon to be released Ice Cream Sandwich, which like Eclair, Froyo and Gingerbread, will work on both phones and tablets and so put an end to Android fragmentation that Honeycomb exacerbated. So Honeycomb is likely to remain the neglected flavour of Android - think of it as the Windows Me of Android.
-I Programmer, September 6, 2011
UPDATE: Or not. PC World's Brent Rose did an informal survey of Android developers a few months ago and they hit on the lack of tablet sales:
To put it simply, none of the developers we spoke with indicated that the impending arrival of Ice Cream Sandwich is a factor. No one, it would seem, expects developing for Ice Cream Sandwich to be all that different from developing for Honeycomb. If it's going to be running on a tablet-sized screen, graphics will need to be scaled up, and the app will likely have to be redesigned for the new screen size. This is simply the difference between tablets and phones, not between Honeycomb and Ice Cream Sandwich.
All six of the developers we spoke with said, in no uncertain terms, that the reason apps have been slow to come to Honeycomb is that demand just doesn't exist for Honeycomb yet. And if there's no demand, there's no revenue--and no reason to be making apps yet.
-PC World, May 27, 2011