[@ELGainsborough] Ah, got you.  That was my suspicion.  And I have to say, I agree.  Here, you have to trust that players have the skill to separate IC and OOC knowledge, and a lot of times OOC knowledge can spoil the feeling of a surprise.  Surprises are fun, and getting rid of them is not.  However, how much or little is needed in terms of setting and characters is largely up to the DM and to some extent the players.  I will almost never turn down information offered me, and I love discussing details and knowing things, but at the same time, the only things I really absolutely /have/ to know are the governing rules of the setting, the things that I need to be aware of as I shape a character and format their actions and reactions, and the things that character would know.  Everything else might be helpful but it's not required.  Granted, things that would affect how a character acts in a given situation can be a gray area.  And I have some trouble with things that don't make sense or appear arbitrary, as I've had bad experiences where DMs said "this is so and there's a good reason" and then the reason was not good at all.  But in the end, I like a bit of mystery.

Really, my favorite DM has me spoiled.  The group I'm in with him -- and two other new groups we're both in as well, to some degree -- have loads of lore that we've build up over the course of the campaign.  Everyone started off knowing next to nothing about everyone else and just the essentials of the world (though it was a familiar setting for many of us, just moved forward 200 years or so to after a nuclear war and recovery).  So we were comfortable in the setting, familiar enough to be comfortable in our own characters, and could feel out other characters as we went.  And when it comes to surprises, I trust him absolutely -- and with my characters' lives and well-being.  I know he'll ask before doing anything too terrible, and so if he wants to do something and doesn't specify, my usual response is "is this going to cause drama and character development?  If so, let's do it."

Unfortunately, finding that sort of group, and that sort of trust, is not easy.  And because it takes rping with someone to see they are capable and to build that trust, a lot of threads here and other places require exhaustive details.  C'est la vie, I suppose.