I have been emailing my favorite developers notifying them of certain issues. An example, auto wifi enabler doesn't show in the market on 2.3.5. The Dev wrote me back apologizing saying the filters were preventing it from showing, said he'd get right on it, and thanked me for letting him know. Another example is a game that isn't showing. For letting the Dev know he sent me the apk (of the full ad free version) which would work and said he'd fix it ASAP.
I'll bet HBO go has a list of OS builds it will work on and because 2.3.5 is so new, its not included. Email them. You might be surprised at the response.
EDIT- anyone else notice hulu + is also gone? Emailed them earlier as well with no response.