Most musicians create music without making their own instruments. Nobody would question the legitimacy of a keyboard (aka sampler) in a song. Other sampling is just the same principle extended. I respect keyboard players as artists just as much as musicians who play other digital samples.
No, it's not the same principle extended. It is possible to warp a sample out of all recognition, but a great many tunes just use a sample unaltered, which is equivalent to just playing a single note on the keyboard over and over.
Another difference is that manufacturers do not assert copyright over the preset sounds that their instrument makes (although they can and do patent the sound-generation method). On the other hand, creators and publishers of a recorded work do assert copyright over the content of the recording, while not asserting any sort of IP in the methods employed to make the recording.
