Um, are you implying that plastic has some sort of magical warming properties? Sorry, but they both get the same temperature as the outside air. One may "feel" warmer, but it doesn't make it true.
I'd have the say the same thing about plastic when you drop it. A sturdy plastic will most likely crack as well. If it can bend then there is a good chance that it will distort in heat and cold, which wouldn't necessarily be good for photos and sharpness.
Don't be ridiculous. It's known that some materials absorb the surrounding temperature more than others. How else would a coat keep you warm? How is "feeling warmer" any different from "being warmer?"
Yes, not all plastics are created equal nor are all drops. Hence my use of the word "can" and not "will." We have to trust the lens designers to provide us with a plastic that has a favorable characteristic for optics - the same way we trusted them for the metals. Metals expand and contract with temperature changes too. Heck not all metals are even created equally.