Probably because the N900 had a fabulous resistive touchscreen, accurate and able to detect the amount of force being pressed against the screen. The accuracy allowed users to target extremely small regions of the screen, so with a stylus you could actually use desktop software (on a capacitive screen, it is extremely difficult to target buttons or move scrollbars unless they are sized-up enormously on the screen). The force detection allowed for painting programs like MyPaint, which only recently have become available on some capacitive screens.

So there are advantages to resistive screens...