That's universal recognizability. Money can't buy publicity like that. DC knows this. And they're not about to let anything happen to their precious icon. Batman can have his back broken, he can change his costume, he can go through any plot-line, but readers know, and parents know, and DC knows that Batman is Batman, and nothing will change that.
Peanuts works on nearly the same principle.
This is why they always seem to possess incredible insight, yet never discover anything new. The difference between ol' Blockhead and ol' Bathead is that the former's strip is based on a formula, where the latter is not. The former is a single plot-line, looped time and again. Charlie Brown's never going to kick that football now, but had the strip run for an additional 50 years, the ball would remain unkicked. Batman's story, however, is written under the impetus of ongoing development.