Ed. said:
Wose are companies like Creative assembly, volition and bioware deliberately hindering modding.
The reason for this is because modding undermines lazy cash grabbing DLC like the empire total war "unit packs" that add six units or the mass effect 2 weapon packs that add five guns.
A mod team would do those for free in less time.
It never hurts genuinely good stuff, the kind of DLC that used to form expansion packs
I don't know about Creative or Volition, but BioWare actually has become [i/]more[/i] mod-friendly in recent years. KotOR and Jade Empire were ridiculously hard to mod. Mass Effect 1 was (as far as I know) literally impossible to mod. Then, BioWare released Dragon Age: Origins with the developer toolset. Mass Effect 2's files were less secure than it's predecessor's and there are threads on the BioWare forums about how to extract files for modding on the PC and the 360 (not sure about PS3, but I don't have one of those so I don't care). And lastly, while they haven't given a toolset for DA2 (yet), they have given advice on how to mod it.
TL;DR: BioWare, at least, has a strong modding community and still has people buying cash-grabs like armor and weapon packs as well as expansion packs like LotSB. People just don't look for the mods as much.