I have a theory about the versions...
Pure speculation, please feel free to throw out your own ideas...
But I believe that Motorola and Verizon asked to be bumped way ahead of the standard rollout schedule for the Droid / Milestone. In fact knowing what they spent on the Droid I wouldn't be surprised if they *paid* Google for the right to do that. (more spectulation! ohnoes.) This gave Motorola a sizeable leg up on other Google phones, right up until the Nexus One came along.
Evidence for this comes in 2 additional ways:
-How very late Google was in getting the 2.0 SDK to developers
-How many phones are still released on 1.6
I believe that everyone else is still releasing Android 1.6 because if they have a 6-12 month development cycle and they were working on 1.6 before the Droid release date (19 Oct 2009 here in the US), they wouldn't have had time to develop and test based on 2.0+ code and get the product out the door.
Meanwhile, as a G1 user, I suffered through buggy updates as developers scrambled to get their apps up to 2.x snuff and now I'm sitting on my thumb waiting for T-Mobile to push 2.x to my phone. Before summer, perhaps?