Yes, if the iPhone could do a full (usable/doesn't-suck) portait virtual keyboard, then so can Maemo.

But the iPhone can't.

Reasons to do T9:

1) more people are familiar with T9 or T9-style input than with qwerty thumb keyboards.

2) fewer buttons + similar screen area = bigger buttons = more accuracy than the crappy iPhone portrait virtual keyboard.

3) usable one handed -- even the beloved iPhone portrait qwerty requires two thumbs (and, doesn't the iPhone have a T9 mode, as well? if so, so much for the idea that Maemo doesn't need one if they have a qwerty one).