It could be a deliberate MSM attempt to give a bounce to Kerry.
If I remember correctly, Newsweak was oversampling Republicans in their polls since the RNC. Many predicted they would then go back to their usual oversampling of Democrats in order to claim "Kerry is surging" or that "Kerry is the comeback kid".
You remember correctly. This is part of a calculated strategy. Read the editorial in today's Washington Post about the letter they from the woman who said that the debate showed that Kerry was the better candidate. Only one minor glitch: The latter was received via email some four hours before the debate started. If CBS can use forged documents, the DNC (which encouraged letter writers and even provided a sample letter) the rest of the MSM, and liberals in general, can and will use whatever tactics they can think of to paint a rosy picture of Kerry and to denigrate the President.