a) I don't see why Microsoft would support it. They have a model for supported tuner cards for Media Center. Component capture isn't on that list. I don't think you will see support coming from Microsoft. Hauppauage is going to get lucky that Microsoft is adding H.264 support in Media Center, I think the rest will be a backdoor hack on Hauppauage's part.
b) I don't think you have see any problems in Media Center with CGMS-A being output on Component. Does CGMS-A on S-Video = CGMS-A on Component? Again, I don't know.
c) I don't understand what you are saying here, but if your talking about CGMS-A then it's VBI. What "current cards" do I don't know, I've never owned a Component capture card.
Of course, if Hauppauage is taking it upon them selves to hack support into Media Center, then why respect CGMS-A even if it is being output? It could also be striped in the H.264 encoding process.
The key thing here is that Media Center doesn't currently do anything with Component capture as well as nothing with H.264. Both of these would be new to Media Center, and it has not exactly been developed around either. H.264 support is coming, but we have no idea what that in tells from a development perspective. I highly doubt the HD-PVR can parade as a standard analog tuner to Media Center and work correctly, which means it is very likely Hauppauage is going to do something behind the scenes t have it work correctly.