TrueView will view both. It is limited in some of the mark up, etc. abilities, as they would rather have you buy one of the other versions.
Actually, when it was released in Oct '05 (approx), they did not announce it. Word was slipped out on an employee blog. Likely the only reason it was offered was to compete with the free viewers offered by the competition.
I needed the DWG capability to review usable files, prior to passing to the draftsman, as well as a vriety of other reasons.