I believe the reason why they made this combination is that in Germany there is the "rule" that
fantasy + metal = belongs together.
It's simple as that.
I read recently in an Ulisses forum kind user-made list of everyone's top 10 music albums that there was a relatively high amount of metal there.
One commented this as having "good taste". It was implied that both just belong together, and no kind of music is so much fitting people say, like this one.
It's a bit like this: Metal is rather dark music, creating a dark mood, which fantasy also has. And yes, this implies that there is a kind of "mainstream dark fantasy" that's most liked, currently.
Dragon Age + metal music would fit a German point of view excellently, from this perspective it's kind of not quite understandable that they used a Marily Mansion instead.
Brütal Legend is another recent example.
With my personal taste, I often feel like kind of an Alien. I can't stand metal at all, and I'm rather a fan of complex works, like Yes and older Genesis works.
Me, personally, I don't like this kind of promoting metal + fantasy role playing games at all, but that's just my very personal opinion. Because fantasy = dark doesn't exist in my point of view. But currently, dark fantasy is "in", and it appears to me as if this has arrived in meanstream.
That's why "modern" fantasy-based RPGs become more and more dark, I think this trend will become much more apparent in the future. Some German players of Drakensang didn't like its "light" approach at all, instead they wanted Drakensang to be as dark and cruel as current fantasy-RPGs are.
Oh, my.
). 
