That's not entirely true with WinUAE.
I speak from experience. As I said, I often play my games on an emulator and then test them on an Amiga 500. I repeatedly find that there can be problems. There is no such thing as 100 percent emulation with WinUAE. The best example was Phantom Leap before its release. I played it through on the emulator and it crashed immediately on an emulator.