What is the most important point about not seeing a wave in the Senate? Expectations for the GOP in the next two years are very different than they would have been had the Senate flipped as well. Most observers already seem to think Obama will be less willing than Clinton to move to the center, frome where he might try to co-opt moderate Republicans and demonize the rest as do-nothings. Harry Reid and a Democrat-controlled Senate will make that even more difficult.
Here’s a good summary of the idea from one of Ace’s co-bloggers: http://ace.mu.nu/archives/307820.php