The last time I served as a DM, I managed to totally kill off a party, in a game that had been going rather well until that point.
In the encounter when that happened, all the players just kind of waltzed into battle assuming that they would never meet an enemy that would be too tough for them to assault head-on, when in fact I had created an enemy that they were going to need to be a whole lot more strategic in order to defeat. Afterwards, I was a bit dumbfounded that they had all made what seemed to me to be a terribly foolish assumption about the odds they faced.
But in this game, now that I'm a player rather than a DM, there have definitely been a few times when I've thought, "Leigh obviously wants us to take on this particular foe, so I guess I'll assume we're capable of beating it." I try to play my role in a realistic way, but it's hard to avoid having some amount of metagame-thoughts about whether the DM seems to be implying that a particular challenge is or isn't beatable.
Anyway, I guess my overall point is, it's sometimes good to explicitly clarify expectations between players and DM about things like this. Even if it's in the wake of several deaths.
So thanks for throwing the tough challenges at us, Leigh (I know, easy for me to say that when my character hasn't been killed...).
And I'm eager to see who Luke's new comrades are going to be!