Awwww yeah! Missing an Expansion or Stuff Pack? Get it now via Steam for half price! Origin? What’s that? Steam is awesome and dare I say, better? Yes! I say it! I said it! I shall say it again… another time. w00t w00t!!!
NOTICE: Sims 3 Expansions on Steam can ONLY be used with The Sims 3 Base Game from Steam and will NOT work with any other version.
Source: SimsVIP
Remember, only compatible with the STEAM base game, EPs, SPs, etc.
Took you a long time to spot. PS: To buy any EP/SP on Steam you must own the base game on Steam.