I think what they are doing is genius, as many people are holding on to the game for these seasonal races, which stops them from being traded in and sold used (which the developer and Sony don't get a cut of).
So technically the developer isn't providing these free races at their cost, as these seasonal races are providing them additional sales (and profit) from late comers to the GT5 game as they aren't very prevalent in the used game market. My local used video game store currently has no used copies of GT5 in stock (and rarely does), while they have 5-10 copies of new games like L.A. Noire and Infamous 2.
Because of the above, don't expect them to be very forthcoming with news of the cancelling of seasonal races (when and if it does happen) as you will see a flood of these games going in for trade, thus killing the sales of new games in inventory at stores.