Apparently a lot of people have bought DLC from Steam only to find it doesn't work for some reason, whereas using your Steam CD keys through Origin works just fine.
Sign here if you've been afflicted by this and maybe we can finally get Steam Support to take these issues seriously.
Here's the message I just sent Steam Support:
High-End Loft Stuff
Outdoor Living Stuff
Master Suite Stuff
,,,but only the Supernatural and Diesel content works. The Sims 3 launcher claims I do not own any of the other DLCs, even though I can see I own them on Steam and I have even successfully registered all of their CD Keys through TheSims3.com.
Appearently A LOT of Steam users are experiencing issues like this, whereas the games and all DLC will work just fine when the CD Keys are used through Origin. The issue is not related to EA or Origin, it is a Steam issue. Please fix. Thank you.
I strongly prefer Steam, but if I and others have to switch to Origin because Steam cannot take some responsibility for the content sold on its store, it looks unprofessional regardless of how certain you are justified that the blame lies in EA.
Thank you for reading."
UDPATE: While your DLC will eventually work after Steam updates Sims 3 properly (there's no way to force the update after you buy a DLC, I had to wait an hour for it to kick in), the Steam Sims 3 Launcher is still not up-to-date so you can't download content from Sims3.com
or get game updates correctly.