Or maybe he operates in a workplace where you can just pick up the phone at your desk and not worry about the implementation details of the underlying telephony infrastructure.

That was the point. I don't think there are any UCS platforms that encompass all possible good options, though, and people will always find ways to connect via the most direct endpoints jointly available.

Some companies believe that it is better to reject an excellent applicant than to hire a mediocre applicant.

And yet, if you talk to managers, they'd complain at length about the inability to find even mediocre people.

Most states in the US have "at will" employment laws meaning that its easy to fire a person after a couple of weeks if its obvious they're not working out.

That's a false dichotomy. Google has a relative luxury here.

Companies that don't have a large enough pool of quality applicants to hire from need to turn that equation around: rather, they must try hard not to let the excellent applicant get away, as they may not find another.

Of course, but by "some companies", I was mainly referring to Google/Microsoft/Amazon/et al.

I would agree that for the vast majority of companies, having an attitude like that is a losing proposition.