Kaptin M,
At the risk of boring everybody else, I've asked myself the same question you posed about innate conservativeness, and I too often wonder where it comes from. All I can say is that some things should be treated more conservatively than others and perhaps anything to do with air safety is one of those things. I'm not at all sure I agree with you about the ability of the "let's all have lots of fun" cabin crew when the **** hits the fan.
Regardless, appearances tend to be self-perpetuating, and I have to agree with those who suggest that the shallower the presentation, the less respect the presenter will get when it is really required. Perhaps a grossly unfair generalisation, I grant you.
Your question though has made me think and posed a possible thread in JB. Cheers!