You've summed up Nokias problem. I have an N900 and it's probably going to to be the only "official Nokia" example of maemo 5 that ever exists. Not a good idea, I'd feel a lot happier about Nokia going forward if they said they'd do a version of meego for the N900. The UI might not be as nice given that the screen can't support multi-touch but I don't see why that should be show stopper.
They also seem to be suffering from the OSS curse of never quite finishing the software before moving onto the next shiny development problem.
Unless Nokia change their policy I know my next phone won't be a Nokia, currently I feel somewhat stiffed. WP7 looks likely but failing that it will probably be Android.