It's just that Harry Potter isn't the first thing that comes to my mind when 2 people are having sex. The ME series, 2 in particular, did a really good job with the music during those parts.
Well it doesn't come to my mind either if its a normal sex scene, like for example, if they would use the elven ruins song for the scene with Ves, or for another sex scene with no magic and/or comedy, or with no elves and dwarves telling stories at the same time.
I agree with the ME2 reference, the music was fitting and subtle.