The truth is that they aren't always accurate. Take a look at the 2000 elections. If they had been Kerry would've won. Polling is far from being an accurate science. The trouble is that everyone wants to know ahead of time what is going to happen and it's just impossible to really know.
Polling is very accurate when those being polled are those who count the votes.
> Take a look at the 2000 elections. If they had been Kerry would've won <
Oh, really? Who was JFK running against in that year?