Daily Kos explains how to read The Clinton and Obama maps.
As a former John Edwards supporter, one of the reasons I prefer Obama to Clinton is that I think he'll help elect a much better House and Senate. Maps like these are part of the reason I believe that.
This is my reason for supporting Obama as well. I take it a fairly strong given that the Democrats will regain the White House this year. The real question to me is whether the new President will have a Congress (particularly a Senate) that is cooperative or obstructive.