I can't see it this way for a few reasons. For one, I don't see why films within the genre can't be presented in their own ways. Secondly, I think that this whole 'dark, gritty, and grounded' tone is becoming a fad, and in some cases, filmmakers sacrifice a great deal of content for said tone, Dredd being a noteworthy recent example. They got the characterization right, the tone, mood, and violence was on the money, but outside of that...the plot, acting, and writing overall were lukewarm at best. That's not what I want from films in any genre.
The problem is, audiences are giving this practice a free pass, and your last sentence proves as much IMO. There's nothing believable or realistic about the world MoS, TDK, Dredd, or any of these recent 'grounded & gritty' movies present. An overly serious tone, filled with angst and pathos /= realism, but more and more people continue to assert that this is so. Personally, I refuse to put so much stock into the mood of a film; it has quickly become what I'd consider cinematic snake oil.
Lastly, I find the notion that comic book films should forsake the style of their source material to be disturbing. This is akin to my overall issue that people are paying too much attention to the tone of films these days as opposed to the content. If the content and substance that makes up a film is good, then I think tone should be considered a secondary characteristic.