I'm surprised this is just coming to light now. Back in the early- to mid-1990's, there were dozens, if not hundreds, of companies rebranding other notebooks and laptops, and a dozen or so large manufacturers. One thing many of these companies had in common was they liked to cobble names for their machines from a list of prefixes and suffixes. The order would change and form new names, but they were pretty much all the same.
For example, they used prefixes and suffixes like hand, finger, pocket, desk, note, lap, net, power, tough, rugged, book, palm, etc. So we wound up with hundreds of permutations like deskbook, palmnote, lapnote, fingerbook, powernote, etc.
I suppose cobbling two of those names together could make for a trademark, since the words dont actually appear as one in the english language (think PowerBook), but i wouldn't be surprised if someone had already used the term netbook before Psion. And, if that's the case, Psion's trademark is unenforceable.