Most people, unfortunately, learned the hard way that hot things can burn you so the warning message about hot coffee seems unnecessary, although that lawsuit did make me aware that spilling hot coffee on oneself can result in 3rd degree burns requiring skin grafts. Many people do not know there are alligators at WDW and the consequences of not knowing were tragic for this family.
I knew there were alligators in Florida but until my second or third visit to WDW, I thought they were just in the Everglades. I had no idea they could be found in populated areas. Yes I did read a couple of guidebooks prior to my first trip to WDW, but none of them mentioned alligators or snakes that I recall and given my aversion to snakes I think I would have remembered! Eventually I happened to read some posts about snakes and alligators at WDW here on the DISboards and was glad to have that information.
If putting up signs educates those people who, for whatever reason, never knew there are alligators and snakes throughout WDW, I'm good with that.