More than once I've seen a situation where someone has misread their hand and mucked it (I can recall one situation where I certainly did), but unlike something like football where a referee can 'blow a call,' it's the player's responsibility to read his hand correctly, protect his cards, and show when necessary. One thing that is a constant - if your cards hit the muck, they are dead. I've definitely seen a certain 'unspoken' rule about how this sort of thing differs in cash vs. tournament games. It's a lot more likely for a dealer to be lenient at showdown in a cash game as opposed to a tournament game. However, at a recent cash game at Harrah's, a woman requested to see every mucked showdown hand, even if she wasnt in the hand, and the dealer acquiesced every time. Sometimes I don't think it is dependent on the casino - dealers sometimes play by their own rules and unfortunately it can be really arbitrary.
For example, some dealers rigidly enforce the 'last aggressor' rule when showing at showdown, and some don't. I once sat at a table for several hours and heard three different rules uttered by three different dealers about who should show - last aggressor, first aggressor, earliest position...it ran the gamut. It would certainly be helpful for casinos
get together and just solidify the rules, but we all know that won't happen - so, to coin a metaphor, if you come for a football game with a pigskin and everyone else is playing soccer, drop your ball and adapt!