Since voting is very important to stack-overflow users and a lot of users put up answers as fast as possible (just to be first and get the majority of the votes)...
How about if a "null" vote is mandatory?
 mandatory only if you vote on something.
You click on the up triangle for up, the down for down, and the number in between can be used as a null vote (meaning... I looked at this and my vote still goes to the one I up-voted).
 The null vote is only a personal marker (or reference for yourself) not visible to others. Same as "this has been marked as read"
Then if a new answer comes in on a question you up-voted. You will be notified there is a new answer that needs your attention... to be nulled or switch your up-vote to.
If you vote on something... you have to null everything else.
 having all other answers be marked as read (null) if you vote something up is a good idea (it would save time). note: you would still be able to vote on multiple answers for the same question up or down. Like so... You vote something up, everything else is marked as read (null, zero , doesn't matter what you call it) then you can go to another answer (if you want) and also vote it up.
A possible scenario is three answers on a page, the first in gets 10 ups the others 2 or 3, then later a new answer comes in and everyone that voted is notified, so the votes are put on temporary hold until at least half of the voters go back to the page and take a look to verify if the new answer is of better value (it wouldn't be necessary for all to go back, just at least half, majority rules). The notification of new answer wouldn't have to be immediate either, I go back to the questions and answers I am involved with just to check if anything else was said. I'm sure a lot of other do this also? You would just have to visibly see if there is a new question that you didn't null yet (highlighted number?).
I think this is a good idea, it would insure more accurate voting and it would also take care of all the other problems everyone brought up in this other question...
 Also... if there is a late answer it gets ignored by all. This way it wouldn't... So if an unknown finds SO website through google there is a greater chance that using the answers that was voted up is the best choice because it is the best answer.
 Duplicate questions... they are attacked and immediately closed. Late answers are ignored. This solves both problems. A late answer would have the same priority (from people that viewed it and voted on it) as the original answers.
 Programming languages are constantly being updated, do you want stack overflow answers to be set in stone? (and you can't ask another question about it because it would be a duplicate)
 also... this has no affect on people that get together in groups and vote eachother up, they can still do that.