That's what John Harwood's interesting piece in the New York Times suggests:
Nor do [Republicans] fear Mr. McCain’s defeat. His “maverick” stance has long left Republican regulars ambivalent. As Republicans in Congress learned under Bill Clinton, and Democrats under Mr. Bush, opposing a president of the other party can help legislative minorities refocus message and agenda.
“They are resigned to a probable Obama victory,” observed Jim L. Brulte, a prominent California Republican who once led his party’s caucus in both the state Assembly and Senate. Republicans, he added, “understand that that is a necessity in order to set the stage to retake the majority.”
Harwood doesn't give much reporting to back up this idea, but it seems plausible to me. It's notoriously hard for a party to win a third presidential term. Seen in that light, a McCain loss would be the rule (albeit a demoralizing one) rather than the exception. But for Republicans to lose a bunch of seats in the House, again, is the exception. Congressional landslides of the kind the Democrats accomplished in 2006 usually spring back just a bit in the next cycle. If the Democrats significantly build on their '06 landslide this year, that shows just how low the GOP party brand has sunk.