The OP is not asking what the accepted definition of a semi-auto pistol is, he is simply questioning how we categorize things. If I were to put a double action revolver and a DAO semi auto in a black box and had someone fire both, they would likely categorize them as the same thing. They pull the trigger and a bullet fires, every time. However, when you start pulling back the covers to see how they actually work, that is when you start to see that there are inherent differences between them. Thus the different categorization of them. The definitions of the categories help us communicate with each other when we talk in generalities about semi-autos vs. revolvers. However, where do you stop with the categorization? Do you get into numbers of rounds? Trigger action? Types of safeties? You have to stop when it no longer helps the conversation. If you take it to its logical extreme, the finest level would be serial number of the handgun. But it wouldn't help anyone here if I told you I owned a 54338 and a 62775. It's more helpful if I tell you I have a couple semi-autos and a revolver. If people know what I mean when I say that, then we're on our way to talking about something meaningful.