Excuse me for not being supper precise. I should have said the most common use case for TXT requires virtualization.
You are correct. Any conforming code that is able to be launched in a measured launch environment can run in TXT context. However I have yet to see a good example of when this is useful outside of virtualization. Mainly because setting up a TXT context is so expensive. After all its basically a platform reset so you have to stop all CPU's and flush all caches.
I have seen people try to do this but it just seems to have little merit in my opinion. For example Dr. Mike Reiter of UNC Chapel Hill tried to do just that for password encryption. Basically launching a TXT application for every key press (google him for the papers). But the costs seems way to high to me.