I asked a Google spokesperson about this and the response was pretty vague, but the gist seems to be that it will come to other phones once the manufacturers/carriers roll out this Android update. Obviously that could be a while for some devices.

I think there are rumors that the Droid will be getting Android 2.1 (which is what the Nexus One runs) in the near future, but I don't think anyone knows if it will include this update or if it will be what the Nexus One shipped with, which lacks multitouch.