there are guys who do situps everyday. just like guys who do pullups and pushups everyday too.. Mike Tyson used to do 200 situps everyday with a 25 pound weight first thing in the morning
there is a difference between working them out and trashing them. you don't have mike tyson's genetics, nor are you a pro athlete for a living where you can dedicate your life to working out and sleeping and nutrition.
just think about a runner who runs everyday. do they go and do interval training daily? no.. they will do tempo or LSD running. they will throw in interval training every now and then but not everyday
so yes you can do ab crunches daily, just don't trash them.. and if they are sore let them rest