the two counterarguments:
if he gets a major league contract in 2009 but not in 2008, it could put him a year or two closer to arbitration and free agency;
if he goes to a different team next year (e.g., one without a young lefty hitting first baseman like Joey Votto), it could also put him a year or two closer to a callup/arbitration/free agency.
to me, it's six of one/half a dozen. I think that he'll sign, but I can see why he thinks that he has good leverage.