Which is the greater art?

I tell u, actors are lesser mortals than singers. Singers have been known to become great actors, the reverse however seems less probable? Why is that?

I mean just check out Eddie Murphy here sounding like a goat getting castrated!  http://www.youtube.com/watch?v=p_zL2fb4vAQ&feature=related

And then there's Joe Pesci,... this is painfully awffuuullll!!! http://www.youtube.com/watch?v=p4et8Dt6rco

Prove me wrong, but i think singing is a more challeging art than acting. ( at least as far as pop culture's concerned )