So I heard Games Workshop is attempting to treat "Space Marine" as its trademarked phrase.
Presumably they will next sue Warner Brothers for using Orc/Ork in The Hobbit films.
Trademarking "Space Marine" seems perfectly valid from my perspective (though I may be biased as a share holder).
I wouldn't put it on par with words like Orc or Goblin at all, because they're well established in fiction in general. Ork (with a k) however I'm not so sure about. I believe that is a GW invention to distinguish between their two universes (WH and WH40K).
The recent sweeping changes to the entire paint range were done so for similar reasons. While there were technical improvement to the product itself, GW were finding a growing number of other companies immitating their naming convention for paints ("Chaos Black" was "Black Chaos" elsewhere) and so generic words were dropped in favour of characters and placenames from their own prime fiction - "Ultra Marine Blue" became "Macragge Blue", for example.