It is important to remember that Maemo/open source and internet tablets has been an experiment from Nokias point of view. The move from the N800 to the N810 was probably the largest HW vise (keyboar and gps), even though the units are more or less identical in most respects. The N900 is a much more powerfull device with phone functionality, but is still very much an experiment. So even if the N900 will become a practical and usefull device with software updates, it is just an intermediate step towards a "fully functional" mobile computer as far as Nokia is concerned. But, where the N8XX were targeted as a tablet for geeks, the N900 is targeted at technology enthusiasts with emphasis on high end smartphones.

Personally I am not sure where Nokia draws the line between a smartphone and a mobile computer, or if this is only the marketing language for Maemo and Symbian. I guess the concept of pure internet tablets was a dead end, but the concept of a Linux smartphone was not. Maybe Symbian is too complex for low series production high end devices, and Linux is too inefficient for high volume lower priced devices and phones.