My guess....okay, let's say it's the first week of February 09, the Super Bowl's coming up, may be a good motivator to buy the latest football game.

On the shelf at K-Mart you see either:

Madden 08

or Madden 09

If you see Madden 08 you think "08 is over, I'm waiting for the updated game"

If you see Madden 09, you buy it.

Same with the 2K series...the Dreamcast came out 9-9-99, if they call it "NFL 99" they get 4 months of sales out of that before it's outdated.