There is a headphone jack. You just need that weird adapter thing for it and its a HTC thing, nothing to do with Google. The iPhone doesn't have A2DP either.
HTC really likes their ExtUSB thing. The G1 is a first device, and everyone had their share of "We want this feature".
AFAIK, Apple left out A2DP because most of the A2DP headphones out there sound like crap. I'd have to agree, I've tried several and have been disappointed, including the kind that are just A2DP to normal headphone adapters.
Do Google reserve the right to use whatever you do on the phone for research and marketing purposes tho?
That's a question for EULA lawyers, not engineers. ;-) I haven't see what the T-Mobile EULA is yet.