I couldnt agree more about the cup...
I would say in general wilderness travel a cup is as important as anything else in your kit (maybe not the knife?). You can't improvise a metal cup. You could improvise a serviceable knife easier than improvising a cup.
Your comment on the desert is pretty true:
"If I was in a REAL survival situation in the desert and found water, I think I would be inclined to stay there and await rescue.."
I live in Las Cruces, NM. I spend much time in remote desert areas. If there is a reliable perrenial water source (I wish, as of yet I have only seen them in movies.. I have been here on-off for 20 years) there would be a constant stream of animals to be eaten if hungry, water to drink, wood to burn (any desert plant exposed to year round water is gonna be huge) and people nearby or soon to be nearby.
From what I know about Desert Survival, there ain't gonna be any water in the desert that you dont carry into the desert.
I have tried to get water using every trick in the book. I have gotten usable amounts of water 2 times (both from digging!) out of 12+ attempts and counting. And I am doing this with everything I need, under ideal conditions.