According to this article, Games Workshop has made a rather significant move in the realms of legal trademarking...
[url]http://mcahogarth.org/?p=10593[/url]

TL;DR
basically, This guy wrote a book called, "Spots the Space Marine". - Not a WH40k product.
In mid-December, Games Workshop told Amazon that he’d infringed on the trademark they’ve claimed for the term “space marine”. Amazon blocked the e-book from sale.

He's a small indie author, not part of a publishing house, and hasn't the resources to fight it, but would like to start some kind of battle to save the term "space marine" from GW's exclusive usage.

Considering that the idea of the space marine goes back at least to the Lensman series in 1934, and includes such notable sci fi alumni as Heinlein, Cameron, and much more, I think it's unreasonable for GW to try to snatch that term for their exclusive use.