All the polls we see are either of "registered voters" or "registered voters who say they are likely to vote" or "registered voters who are absolutely definitely going to vote and can recite the location of their polling station and voted in the last five elections etc...".
What about polls of anyone who is theoretically eligible to vote (ie: an American citizen over the age of 18)? Are they ever done? If, so, what is the result?
I hate to always bring up the Canadian example, but here when we do election polling we just poll anyone who is a Canadian citizen over 18. Our voter turnout rate is nothing to write home about either (65%), but when pollsters try to isolate people who will definitely vote - it always seems to end up being LESS accurate than polls of all Canadians.
We could hypothesize that if EVERYONE voted, Kerry and Democrats in general would do much better. The again, in Australia they have compulsory voting and had a 90% in the election two weeks ago - and yet that the ultra-rightwing Bush-clone John Howard still won.
So go figure.