Or decide at the last minute. But I'm not so concerned about the accuracy of polls. I'm concerned about journalists using polls to frame their stories. Journalists covering the presidential election check four tracking polls every day. This gives them their fix of who's up and who's down since the previous day.
Polls provide the framework on which the stories hang.
Take away the framework, and the stories collapse. There are many ways that journalists can frame campaign coverage. The campaign in 1992, for instance, was framed in terms of the economy. This year's frame is the close election. This is written in the newsroom, not the stars.