Yes, the author is American. GW's trademarks for "Space Marine" are registered with the USPTO, so I'm not sure why you even bring that up.

They could send letters to Blizzard all day and not be in any trouble. Blizzard would just ignore them. Is Blizzard going to sue them for sending a letter?

Now I'm not saying I'd run my business like GW does, but your blind hatred of them is just silly. The one to blame here is Amazon; they should have just ignored it but instead they kowtow to every media company out there at the expense of the little guy.