Yes, like Ianion said, there are different classes of THX certification. The classes concerning home theater are 'Compact', 'Select', 'Ultra', and 'Dominus' (outlined on
this page). The multimedia stuff is basically for desktop PC stuff from when THX was owned by Creative Technology. But it's not necessarily a bad thing. THX doesn't necessarily mean blazing loud big screen sound. It's more like a way to be sure that the content is being seen and heard in a way that its creators intended. So if you are a content creator working to create media for a desktop PC environment, you will necessarily be working under some strict limitations since most desktop PCs can not accommodate a kick-ass sound system (mine can). But if the content is THX certified, and the desktop playback stuff is THX certified, well then at least you know you are receiving the media in a matter that its creators intended. Sure, it was just a way Creative (and now Razor) can put a THX logo on small audio systems, but it could still theoretically have value. I am not sure it was ever used to its potential though.
But as Ianion said, the home audio stuff and PC stuff are two totally different classes of certification.