My games are usually a high 3 or a solid 4. This is because my DMing style is very much "let the dice fall where they may." I rarely cut players a break in terms of fudging die rolls or selectively ignoring the rules, since I like to stick to the rules as written most of the time (sometimes, I might "forget" to have a monster take their action in a round, but that's about as far as I go with handing players a break). I wouldn't dream of fudging die rolls or rules for my monsters to get an advantage, so I don't think it's fair to do it for the characters either.
I also tend to run "status quo" settings, where the APL is not the major determination of what is to be found in the setting. Trolls are common in the Troll Hills because that's where they live, not because the APL is around 9 and that's where the characters happen to be adventuring. If the characters want to venture into the Troll Hills at APL 3, I won't stop them--but I'll certainly regale them with tales they hear in the nearby settlements of horrific troll raids and adventuring parties that went there and never returned. If they still want to go there... Well, they can't say they weren't warned.
My D&D worlds are brutal places where you risk serious consequences for doing risky (or stupid) things. As a DM, I feel like I have a responsibility to impartially adjudicate how the world works, not to allow characters to try anything they want without consequences. If you really want to slap the princess at a royal ball or try to break into the assassin's guild headquarters, I'll let you try it... But there's no "reset button" or "loading from your last save." You're going to have to deal with the consequences.
That being said, I rarely put things into the game that can't be handled multiple ways. Combat is always risky, but I try to make it so that the characters don't have to beat everything to a bloody pulp to advance the plot either.
Character death is actually very rare in my games. I've only had one in my 4E game so far, and it was totally avoidable. I've noticed that players take their actions seriously.