There are misleading teaser covers, and then there are just plain lies.
I think it's safe to say that most comic covers exaggerate the content of the issue to sell copies. Sometimes they pick-out what turns out to be a non-event and blow it up on the front cover (Good example: Catwoman #19).
Sometimes it's something that's really more of a misunderstanding, or something that sort of happens, but not really (usually involving a shape-shifter, or some sort of mind-control, or a hero purposely acting like an ass because it's the only way to save a bunch of people). (Good example: Astonishing X-Men #14).
Sometimes it's more like an artistic summary of what happens. So the scene on the cover never actually happens, but it's figurative (Good example: the latest crappy issue of Detective Comics, #823).
But then there are just plain lies.
I bought this comic yesterday because the cover is completely awesome:
Here are some things that do not happen in this issue:
1. Superman does not ever try to pull Batman's mask off for any reason, or imply that he is thinking about doing it.
2. There is no mention of the fact that people will die if Batman's face is revealed.
3. Superman and Batman are never in their costumes at the same time.
4. Though they are in a castle for much of the issue, neither it, nor the people in it, look so medieval.
5. Superman and Batman don't even disagree once in this story, let alone end up in a position where Superman has Batman in a headlock and is forcing his mask off.
Is that not the most haunting facial expression you've ever seen? I can barely stand to look at it. And yet, I cannot look away.
Jesus. Now I've got the jeeblies. *shudder*