Well do a search for the word Unobtanium in that wikipedia article.

You will see it is actually 50/50 on the spelling. Scientifically Unobtanium is the correct nomenclature IMO.

I mention James Cameron because he does extensive research for his films, and he even created a fully functioning language around the navi people which was rumored to take almost an entire year. So, I would trust his research over a wikipedia moderator for an obscure article.