a) it fools people into buying the same game twice
There may be one or two people who get fooled, but most won't, and although I dislike some of EA's business practises, I'm willing to give them the benefit of the doubt and say that I doubt it's their intention.
Your (b) may be valid, but I suspect this is more in the way of a marketing decision. As can be seen by the mass "gold" announcements, christmas is the season to have your game noticed. Despite the recent expansion(s), The Sims 2 wouldn't have much press if they didn't do something like this. By re-releasing the game (with a few extras), they can ensure that it's on store shelves, and gets some decent advertising.
Personally, my only objection would be pricing, but since we don't know what the price will be (although most likely 'full'), it's probably premature to go apeshit over it.