I don't think it's that Kelly Clarkson for example can't hit the notes it's that the whole "auto tune" sound is popular now so the add it in as if it we an instrument.
What number is it at on the overall iTunes chart? (not the pop one) I can't check.
edit:
I didn't know I could check online! He's #13 overall!
https://www.apple.com/itunes/charts/albums/