It's more likely that it's because the underpinnings of the 922's OS are completely different from whatever the 722k, 622, and 622k run. The hooks still need to be put in for the Revue to tie into. And since they were already busy getting the 922 to be more reliable, stable, and feature complete with S109, they decided to get that out first instead of making us wait longer by adding GoogleTV integration into that update in time for the Revue release.
There shouldn't be any hardware reason why the 922 wouldn't work with GoogleTV and the calls to the 922 asking for DVR data should have a minimal impact on it's performance. It works with Remote Access and GoogleTV is asking for the exact same information as the website is.
I agree. I also think Dish is doing the right thing, by trying to squash some 922 bugs before they put something else into the mix. The 922 is slowly becoming a reliable box. I only have one friend who has one, but he has not missed a recording since the last update and that was a big complaint of his.