I've read a lot of comments on here about Warhammer, Tolkien and other stuff. So here's the right answer from someone who played tabletop games before the internet was invented.
Gamesworkshop used Orc for it's Warhammer game which has a medievil fantasy setting. EDIT where they ripped off Tolkien.
They used Ork for Warhammer 40K which has a science fiction setting. EDIT where they ripped off all previous forms of science fiction and fantasy and mixed it all together into sweetness.
I presume it made stock keeping and advertising easier, I wouldn't read too much into it.