first off, you qualified it to small donors to George W. Bush. I'm not saying ol' Georgie isn't taking in globs of money, he's far and away the leader in the pack with $84 million.
Hell, ol' Dean is only second at $25 million.
But like I said, you qualified it to small donors. FEC documentation only requires that people be listed if they give $200 or more. However, FEC documentation DOES require that the total amount from $200 donors or less be given.
In George's case - [link|http://www.opensecrets.org/presidential/donordems.asp|11%] of his funding (individual) came from donors who gave $200 or less.
So, taking our [link|http://www.opensecrets.org/presidential/summary.asp?ID=N00008072|$84 million], multiplying it by 11% give us roughly $9,240,000.
Dean on the other hand has raised [link|http://www.opensecrets.org/presidential/summary.asp?ID=N00025663|$25 million] and [link|http://www.opensecrets.org/presidential/donordems.asp|56%] came from $200 or less contributions.
$25 million * 56% give us $14,000,000.
Which, as you pointed out, tell us nothing about the number of donors.
We do know, however, that the minimum number of donors for Dean would be if each doner gave the max amount - $200. ($14,000,000 / $200 = 70,000).
And we do know, however, that maximum amount of donors for Bush would be if each donor gave $0.01. (One cent). ($9,240,000 / $0.01 = 924,000,000)
So obviously, Bush has 13200 times (924000000/70000) more donors than Dean.