From the NYT article on the GPhone:

“Running a Web site and a search engine is one thing,” said Mr. Weide of IDC. “But developing a phone is a whole different game. It will not be easy for them.”

There's a flock of nerds who originally worked together at Be, Inc (the BeOS folks) and then went to Danger, where they made the hiptop (a.k.a. T-mobile Sidekick). Once the hiptop shipped and became boring some of these folks splintered off to form Android and at least one (hey, Jeff) went to Apple to make the iPhone.

Google then bought Android, so if the Goog wants to ship a phone they can ship a phone.

Pure speculation: I'm betting that a lot of the Danger guys are so peeved that the hiptop developer community was totally crushed because of braindead carriers that they're going to make it right this time by opening the platform to third party hacking, even if they have to circumvent the carriers.