You presume that Bush will have the stomach to veto anything. I'm not so sure he has it in him.
You make a very good point, which is why I was careful to say the vote will not be veto proof, not that Bush would actually veto the measure. I have no confidence in Bush to do the right thing. He's just drawing a check like 99.9% of the poiticians at this point.
Distinguished Representative Murtha promises to embed his near-fatal poison pills into appropriations legislation necessary to fund our troops. If Bush vetoes the bill, then the troops get no funds whatsoever (unless Congress tries again). That option tactically might not be his best choice. Any veto also could enrage the Congress into impeachment, which requires fewer votes (in the House) than overriding a veto does.
Bush at this juncture has the power of a starving prisoner given spoiled and partially poisoned food. He can eat it and bear the consequences, or he can return it and beg for something better. If he elects the latter, then his jailers could give into his requests, but they more likely would deny him food altogether, increase the poison dose, or even perhaps beat or execute him.
If the poison is not strong enough to prove fatal to our standing int he Iraq theater, Bush probably should sign the measure and bear the torture. Going to Congress for war appropriations is analogous to begging your enemy for the bullet that kills him.
Given all the trials and tribulations of his office, President Bush still is practically the only man in Washington with our needs at heart. He may get it wrong much or even most of the time, but almost nobody else ever even cares about this existential battle for Western civilization except those who actively work on behalf of our enemies. It's lonely and isolated at the top, and we pray for divine guidance, wisdom, mercy, and strength to come upon our President.