Truth in all the above statements.
All the parts vendors have a tough job. They are at the mercy of their suppliers, some of whom are less than great.
I know Carl tries to source American as much as he can. Don't know about KW.
The main difference I've experienced is depth of knowledge. I've called KW and not gotten intelligent life at the other end of the phone. In fact I've sent them corrected information on more than one occasion, which in one case they haven't bothered to include in their catalog listing. Go figure.
Carl, on the other hand, has always given me what has turned out to be correct info. He may not be perfect, but I've had much better luck talking to him rather than to KW. Talking to Carl is like talking to Herm the Overdrive Guy. He knows whereof he speaks.