Creative Assembly's Craig Laycock stopped into the Total War Center forums today to deliver some bad news but tasty mod files; he says while their Warscape engine has gotten too complex to allow releasing a conventional toolset easy, they are able to make XML and XSD files available for Empire: Total War and Napolean: Total War, which is certainly something if you're a modder or love to tweak.
Though it's understandable fans figure the lack of modding love from studios is a ploy to sell more DLC, Laycock states it's definitely not the case with them ("if that were true, there never would have been the possibility of making unit-packs for Empire and Napoleon"), it's simply a matter of technology and resources.
As for Shogun 2, they're still looking into how to promote modding there, but want to wait they reach something final before promising and then not possibly delivering. So, we'll see.
Anyhoo, if you're into such things, hit the source to grab the files. As always, mail us if you come across or create any particularly awesome mods or tweaks.