The reason might be that they're planning on bringing a whole range of devices with Harmattan. If that were the case, they would have to also test the phone aspects of Maemo to get it right, so it would explain the smaller size of N900. With Harmattan they should have all the experience and pieces together to make great devices for both phone and tablet use. It could be that the current tablet hype just caught them off guard. I'm hoping there's some rational plan behind all this rather than just a screw-up