Personally I don't think HTC can afford to drag their heels on this one. They got away with it with HTC Hero, but it won't fly with the HTC Desire. Some people are already refusing to buy the HTC Desire, because of their laziness with getting 2.1 on to the HTC Hero. It has already damaged them from a customers POV.
No, I reckon they'll work as hard as they can to get 2.2 out to Desire & Legend.
I'm too looking forward to the UI reset from Google. Should be very interesting, I have never used stock Android UI. But surely it can NOT be that bad as some people are making out?