I'm not a graphic designer so I can't speak to why this works, but it's pretty neat.  
  

I think in the case of Batman it's mostly just luck/coincidence that it works. The logo isn't designed by professional designers/marketers who are carefully trying to craft a certain response. It's literally just whoever happens to be drawing Batman at the time draws the logo on his chest in whatever way he desires. Kane (who invented Batman in the late 30's) wasn't a designer or marketer in the slightest. He just decided to throw a black bat on Batman's chest.

I suppose in the case of the movies the logo is carefully pondered, but most of these variations came from the comics themselves.

I think part of it is that they've allowed it to change and evolve which is unusual for companies.

I remember working with Shell. They have three volumes of rules on how you can treat the pectern (the Shell logo). No colour changes, proportion changes, definite rules about handling it on different backgrounds, about it's use if different contexts, about use with text... On and on.

Ironically if DC had been like that they'd actually have a far weaker brand.

Fun fact: through the years, Royal Dutch Shell's logo has changed quite a bit. It started as a depiction of a mussel shell, the current scallop shell logo came as recent as 1971.

"the pecten symbol currently in use worldwide was designed in 1971 by loewy. the design and testing process completed by loewy's firm took more than four years. one of the tests involved hanging various prototype pectens on poles where they could be viewed by drivers passing on a nearby british motorway. drivers were later contacted for their opinions on the prototypes."

http://www.designboom.com/portrait/loewy.html

If we're doing fun facts: Salvador Dali designed the Chupa Chups logo (the little lollies, like Kojak used to suck) back in 1969.

Improbably but true. I'd link to their website but they've turned the whole thing into Flash so I can't. Their design has clearly been going downhill since 1969....

It's extremely common for identity rules like that to exist for a company. In my experience a company hires a hotshot, really kick ass design firm to design their identity and branding. And the end result is pretty much a tome of rules and examples on how the branding can be used in just about every conceivable situation. From there the internal design teams take it and utilize it.

Those guidelines are extremely useful when you need another third-party to do work. Otherwise they are likely to want to express themselves in your logo. For internal use, with a deep brand understanding, you should allow your team to be more flexible -- to stray, they should have a reason.

Do you have any evidence which suggests that third-party creativity w/r/t your logo is bad for you? As one example, I see all kinds of websites with reddit/digg/twitter/facebook buttons that have been restyled to fit the design of the website; I really can’t see how this hurts those brands.

(Or do you only mean third parties working directly on your behalf? I suppose in that case guidelines would be important.)

yes -- working directly on our behalf -- designing a tradeshow booth, an ad, a giveaway. They expect us to send logo guidelines. Our guidelines are simple (just a couple of pages) -- Just showing how to make it monochrome, and some acceptable variations.

Let's not forget Firefox's rules

It works because bats are animals and inherently dynamic, so we're accustomed to seeing them from all angles. We've been conditioned to recognize many different shapes as "bat".