At this time, some are comparing CM Punk's status in WWE to Bret Hart in the early 90s. Punk is considered a workhorse, but while he is the champion, he usually does not get top billing over John Cena. Hart had to battle the image of Hulk Hogan back in the 90s.
There is also some concern that Punk may become worn out due to how hard he works. That is a concern for the company as they only have two legit top draws, Punk and Cena.