Why Do Some Upper Arms Look Round And Others Look Rippy? (pics Included)?

Okay so look at this one below, the arms are nice and round and full.http://www.contactmusic.com/pics/m/i_am_…
In this one the arms especially the guy in the middle and right look not round and weird shaped, like the guy on the right has like a bend.http://imagecache2.allposters.com/images…
I’m just wondering the reason for this difference?