Almost, first, you got a visa exempt entry for 30 days (not a VOA), then you applied in country for an initial Non-B visa, then you applied for a yearly extension of stay, and it is that extension that was cancelled.
Sorry, but you are wrong. What you are calling a visa, is actually an extension. Extensions are cancelled, visas are not. This is why mods check posts, so that incorrect information is not passed on.
99% of YOUR employer's maybe, but that is most certainly not the norm. Also, I have never had an employer ask to keep MY work permit, so again, you are just talking about your experience.
You are pretty well spot on, BUT the work permit belongs to the employee, NOT the employer, and it is the employees responsibility to ensure it is cancelled