Nah. A movie's success or failure is based in part on the acting therein. Acting typically involves the use of one's voice. Therefore, it's a perfectly legitimate line of criticism.
Would, for example, "Dirty Harry" be as good a movie (if at all) if, instead of Clint Eastwood growing "did he fire six shots or only five" you had, for example, Paul Lynde lisping his way through the part? Of course not (well, maybe for Rob).
Also, as you might recall, my reaction to Howard's voice was not that it ruined the movie, only that I found it slightly off-putting and that I thought Cheadle was a better choice.
