Obviously the Senate doesn't take the White House's talk of a veto very seriously. Why? For starters, we're five years and three months into the Bush presidency, and he hasn't vetoed a single bill yet.
The Senate's action is Pavlovian behavior. Senators have learned from experience that Bush advisers tell the press that the president "won't accept" a bill whose spending exceeds a certain level, only to see Bush sign whatever they pass.
Remember last summer's transportation bill? The final bill that Bush signed into law was $30 billion more than what the president had said he wanted.