@Hades32,
The Opera version on the N800 (or rather OS2007 and older) is a mobile version, i.e. no integrated email etc. It would be much bigger and slower if it had (the memory footprint would probably be much bigger too).
As for the second question: Linux runs on many (a dozen at least) architectures, so just 'linux distro' won't be enough. The versions you're thinking of are for Intel x86-based CPUs (i.e. Pentiums and compatibles like AMD), while the Nokia internet tablets use an ARM CPU (very common on mobile devices because it uses way less battery power). So, those versions can't run at all on the N800/N810.