It's money.  Obama gets to tap his big donors twice: $2,300 for the primaries and $2,300 for the general election.  Last month, the inexhaustible well started to dry up.  They have $250 or $300 million that opens up once Hillary is shoved out.

Otherwise, Obama is very much better off letting things go on to ther convention.  The Hillary-Pbama battle freezes McCain out of the front page and takes away his earned media on TV.  Since he can't raise money, that's a crucial hit.

Look at the MYDD electoral vote calculations every day.  McCain has been sliding down, not gaining, during the Democratic fight for the nomination.

Take the money out of the equation and Obama, Hillary, and the Democrats are much better off taking this to the convention.