Yes it may stagnate but sometimes someone will make work that is exceptionally interesting and exciting while staying within the constraints of a style. I think the real culprit for dissatisfying clients is not simply brainless adherence to style. I think it has more to do with an arrogance that some designers have. The perception that they simply know what is best and that the client is a pleb if they critisize or complain or simply disagree. This is so very wrong.
Clients are a designers business.
You need to make something that they are happy with. This arrogance may show it'self as a stubborn adherence to a style. But let's not blame the style, blame the designer. It should a case of the right tools for the job, or more correctly, the right styles for the job, not satisfying your own ego. Paramount is that the design must fit the job, and ultimately the client must be happy with the work that you do.