All the other N-series devices run S60 and all have more or less the same capabilities and built-in software. Adding support for a new device is probably very little work for them. I'm guessing that they just need to test and possibly do a few tweaks to accomodate a new screen resolution or work around some software glitch in the firmware.

The N900 is another beast altogether since it runs a completely different operating system and has a completely different set of built-in software and libraries. I too hope that they'll consider supporting it but the fact that they support the S60-based N-series is little indication that they'll support the N900 unfortunately.