This is good stuff. Getting me thinking hard about my ideas.
"when was the last time you saw a hardened steel bushing for a temperature sensor? You haven't because they don't transfer heat well"
I don't think that is it. I think it has more to do with the fact that steel (hardened or not) is more easily corroded than copper, brass or stainless (and perhaps other metals commonly used in this application.)
On temp sensors, copper and brass are generally used because they transfer heat readily, are malleable, maintain their strength (don't crack) through repeated temperature variations and are extremely corrosion resistant. Stainless is also used in these applications.
"Please explain how you can have a piece of aluminum that is the stiffest but the softest at the same time....."
It has to do with the dimensions of the material. The piece of aluminum that I would have to use would be larger in diameter and with thicker walls than the steel. It would be measurably lighter even though it has more mass. Softness and stiffness are not necessarily an equal relationship. If I am using 6061 aircraft aluminum it can be pretty hard in terms of aluminum, but not in terms of steel. Does that make sense or am I an idiot? (be nice!)
"I weighed 165lbs in high school when I bench pressed 315 but the guy next to me who weighed 220 bench pressed 400...who is stronger?"
Um. The other guy. But you are talking about two humans.
I would compare aluminum and steel to be more like a human to an orangutan (OK, stop laughing and clean the beer off of your monitor). The two metals are as different as the two species, aren't they? As I said earlier it is not a linear comparison. Orangutans are roughly the same size as humans (adult males weigh around 200 lbs and the females weigh less) but they are well recognized to be a great deal stronger than humans, one internet reference (you can believe anything you read on the internet!) says they are four to seven times stronger than humans! (Answers.com - How strong are orangutans
Enough monkeying around, I'll do more homework.