Price change in the Sims 2 expansions?

Just out of curiousity, why did the expansion packs for the Sims 2 recently drop in price? Just a month or two ago I was in Wal-Mart looking at expansions and noted that they all ran around $25-$27. Last week I was in there and they were $14. I almost fell out right then and there (and the proceeded to buy Pets and Free Time, hee hee). Just wondering if this is a short-term thing (holiday season and all) or if the prices have just gone down on them (meaning, if I come back in a couple of months, will it still be low?). Thanks!