They got about the same width (due to the different aspect ratios) which is offsetted by the increased accuracy that the resistive screen on the N900 has.

Btw I have used it for a little while both on nemo and on maemo and it is usable. The most annoying thing about the portrait vkb is the edit window. It should be split screen imo, not overlay. The nokia im system allows split screen keyboard (see the stylus keyboard on Diablo). This is something worth exploring.