nope.
Some other fabrics are as good (if not better than cheap leathers) in accidents. Some are designed to melt with road friction, and allow the rider to slide down the road as opposed to "dig in" and others have a stronger structure, and dont rip/tear so easily.
As to whether "somethng" should be made compuslory to wear? nah, i dont think it should. Helmets save lives, leathers stop scarring, road rash and prevent bones being broken (with armour). The people you see in shorts would be terribly wounded/scarred if they came off but it PROBABLY wouldnt make a nonfatal accident fatal (assuming they got prompt 1st aid).
As for myself, never go out without leather (armoured) jacket, gloves and helmet. If i'm doing more than say 2 mile, or not riding in the town/city (ie go slower in towns/city) then i'd at LEAST put jeans on.
More than trousers, i'm amazed at the number of riders i see without gloves.
Fall over, and see what the first thing you put out to stop you is...