Sorry if I come across as over-reacting...it's just annoying. It's just that I put as much mental effort into some of these shots as I would through a camera - light, composition, exposure, etc etc. And I undertand "Bioware owns the copyright anyways," but when I take a picture of a tree, it's not like someone can say the copyright is owned by "da bears." 
I can see why watermarking a screenshot is a grey area because unlike a landscape, the subject of your "photo"
is someone else's work. Copyright is irrelevant; the bears didn't labor for days to make that real tree the way BioWare's artists labored to make that digital one, and I'd be annoyed if I worked at a game company and saw a screenshot watermark that came off as someone else signing my art. However, I don't really ever post screenshots at ToP, etc., because they're usually not watermarked and I don't want to offend people who put a lot of effort into a screenshot via flycam, performance mods, headswap mods, etc., so I wish people who did something that requires extra effort and would like credit would watermark it.
If you're concerned about coming off as claiming credit that isn't yours, you could always watermark it "Screenshot by [you]" to make it clear that you're not claiming credit for BioWare artists' work, just the work you put in to compose the shot.