Actually I do see a difference. Many of W's gaffs were funny, entertaining at the very least. I never made the leap from he's a little dorky to he's an idiot POTUS. They were like two separate issues. At times he WAS an idiot POTUS for some of his command decisions, my personal opinion.
It seems to me the humor is much darker with Obama, no pun intended. O's personal gaff's just don't reach the level of "funny" that W's did. All though, Biden brings me hope, now that guy can be funny at times!