Why?
His statements now and have been putting the pressure on Kerry to stop all 527's.
With Bush's comments, Kerry now has soundbites for an ad in which he can say that "even George Bush has attacked the Swift Boat Vets...even George Bush says Kerry 'served admirably...He ought to be proud of his record.'"
By giving Kerry these sound bites, the President has helped marginalize the Swift Boat Vets.
What Bush should have said was "I am calling for an end to all unfair advertising and ask that my opponent do likewise" and shut up.