The point is they respond by saying, "Me too, but much, much more." To the average voter the bottom-line numbers are forgettable. What is remembered is that Bush wholly gutted the Democrats' argument and denied them even a fraction of the force inherent in the issue. I believe it's great politics even if I don't fully agree with the policy when viewed in isolation from the politics and the larger picture.
This came so unexpectedly, in a major speech, that no matter how much money goes to it, Bush will get the credit. Mind you, if I read Bush's body language and tone of voice correctly, this was second, only to taking out Saddam, in his personal priorities. If the Dems ask for more, he'll let Congress argue it out and signoff on however much they put into the budget, $15B or $35B.