Quality? In what sense?
I don't get it, that statement is of complete opinion. Are you saying people are wrong for holding that opinion?
Let's put it this way:
I don't like Starcraft II. But hell, that's a quality game right there.
I don't like Metallica. In fact, I usually avoid it like the plague. But damn, that's some damn fine guitar playing.
I like watching Dragonball Z episodes, but it is by no means the best animé out there.
In this way I too find Oblivion very relaxing and great listening music; that's my opinion. But as a soundtrack it's unfortunately not the best.