Hillary Clinton is in Indiana now, but she spent the first two-and-a-half days following her Pennsylvania victory in North Carolina. I don't think this is any coincidence.
The Clinton campaign's strategy at this point is pretty simple: maximize the number of popular votes she receives over the remaining primaries. The more popular votes she gains, the more of the myriad number of versions of the popular vote count she'll have an opportunity to tout a lead in to the superdelegates. And by this measure, a vote in North Carolina matters just as much as a vote in Indiana.
True, if Obama wins in Indiana -- I would expect the referees to step in and end the fight. But if Obama wins by 20 points in North Carolina and loses by 4 in Indiana -- the race will be just as over. Obama would have wiped out any popular vote gains that Clinton made in Pennsylvania, and eliminated any opportunity she has to beat Obama in any of the more widely-accepted versions of the popular vote count.
In most respects, the nomination process is a zerosum game, so if Clinton is devoting, say, half her time and energy to North Carolina, one might expect Obama to do the same. But the race for the nomination is not the ultimate goal -- these are the semifinals in the race for the Presidency. Obama can still win a 'clean' victory by winning Indiana (and probably only by winning Indiana). And a clean end to the nomination process will, in my opinion, ultimately buy him a couple of points against John McCain (at the very least, it will buy him a couple of weeks of good press, instead of the bad press he'll have to endure when the assuredly lopsided numbers come in from West Virginia and Kentucky).
But the Clinton campaign can only win a 'dirty'/disputed victory -- style points do not matter them. And that means going where the votes are and letting the chips fall between different states where they may.