A quick glance at the exit poll numbers supports your view. In both 2000 and 2004, the same percentage of Democrats voted for Bush -- 11%. Of all voters who voted for Gore in 2000, 9% switched over to vote for Bush in 2004. But that's cancelled out by the 10% of Bush voters from 2000 who voted for Kerry this time. It doesn't look like there was any significant net erosion on either side.
Good stuff. Thanks