I'm sure the writers of these songs did not intentionally write sour notes to be sung, so what's the deal? Some of these bards are so awful at singing, I have to ask them to stop mid-song. Notably the one at the Bannered Mare in Whiterun, especially when singing "Tale of the Tongues". I mean, that song is supposed to be about me, and he butchers it every time! I can't stand it!
I know I might be picky, and this might not bother other people, but I just cannot stand hearing all these tone-deaf singers! And these bards are supposedly educated at the "prestigious" Bard's College? I laugh whenever they tell me to go check it out. Why, so I can learn how to sound like a dying cow!? Well I hope tuition's free, because I can get better singing lessons from the bandits in the nearby cave!!!
Someone just needs to get Malukah to re-record all of the songs to replace the ingame ones. (If you don't know who Malukah is, check out this awesome video: http://www.youtube.com/watch?v=4z9TdDCWN7g&feature=related)
So yeah, that's my two cents. Get some better singers next time, Bethesda. Jeez.