Pop out the battery of the N900. Hold it in your hands. Maybe toss it into the air a couple of times. See how tiny that little battery is? So how long do you think your dual-core 2.2 ghz laptop would run on a battery that small? The defense rests their case, your honour.
Qt with total compatibililty with Maemo and Symbian is already here, as of a week or so ago. The big part is getting WinMo's compatibility up to speed (Not sure if they're still supported, but they were in past builds), and maybe RIM and Android ports of Qt. Then they can all use branded versions of the Ovi Store. That sounds like some world domination stuff, and it is. No one can address as many devices and desktop systems with one app framework other than Java, which sucks, other than Nokia. So everyone making apps, this is the holy grail.