To answer the first question: "Why are wrestlers so tough?"
As it's been said, a good part of it is mat time but it's not just the time, it's the QUALITY of the time. Wrestlers undergo absolutely BRUTAL practices every time they step in the wrestling room. They make weight weekly. They train constantly. To get to be the captain of any halfway decent team that guy has not only put in mat time, but he's put in time being punished hard and rose to the top of his team. That's work ethic. Secondly, one thing that has always fascinated me about wresting-tough versus other-guy-tough: wrestlers don't spend all their time lifting weights. They get their strength from functional movements. They get it from throwing other really strong guys around for years. Their strength comes from controlling another guy's bodyweight using their own body position. In jiu jitsu we preach position first -- that's all wrestlers do. They get position and keep it. That's a whole 'nother kind of tough that you can't get from just lifting heavy things a lot. The only way to get that kind of strength is to spend a LOT of time moving other tough guys around (or have a strength and conditioning coach like Greg Walsh who understands functional strength

).