Troy does change, though. In the beginning, he still cared about putting on a tough guy front, but after spending time with Abed, he just stopped caring. His transition was finalized in Epidemiology, when he sacrificed his image to wear the nerdy costume in an attempt to save everyone.
--
http://img94.imageshack.us/img94/4418/dsc02035h.jpg
http://i38.tinypic.com/2zqtqur.jpg