Each poll is an individual snapshot. You can't just add them together and use that to reduce the margin of error to nothing. Probability and statistics doesn't work that way. It is fashionable to add different polls and average them, but that really isn't statistically valid.
But don't you have to take into account that all the polls are basically saying the same thing---Bush is ahead 3-7 points---Doesn't this help to validate the polls to show that Bush is indeed winning?