Would you expect a WinAmp clone to comply with Apple's user interface guidelines?

The original likely infringed all Windows design principles.

Yet they pulled off one of the most usable media player.

Windows users don’t care about Windows design principles because there basically aren’t any.

At the time there were. Between 1995 and 2001 or so most Windows applications had largely consistent interfaces (yes i can think of exceptions, like WinAMP :-P and even Microsoft's own Office didn't always follow the rest of the OS, but in general at the time following the OS style was considered desirable).