If the salespeople have no idea (and truthfully, they usually don't and are never told anything) then why punish them? It's the sales managers who (in my experience) are the ones who push and lie and deceive. And yes, not only do they not respect the buyer, but wasting time is one of their techniques to tire you out so that you make a poor decision.
Only to be trumped by the F&I managers, who sell you the warranties and marked-up finance. That's where most of the profit is these days, especially with used cars.
BMW and Porsche also have cars that they use just like SM, but to my knowledge they do not block the warranty on them.
That's pretty crappy, GM.