My opinion on the matter.
For the Most part, I agree with you PanVac, however, I think there are *some* instances where direct-air machines can be used in commercial applications. For example, I have an Oreck XL9100, and I've relegated it to being a "quick clean-up vac for me. Like, whenever I don't feel like bringing out a bigger machine of mine, I'd use it instead. That's kind of my stance on machines like those in commercial settings. They can make good quick clean-up vacs as long as you don't pick up anything too large or gross for it. Also, they should only be used with disposable bags, no dump-outs, period. Also, vacuums should not be used to pick up large amounts of food particulate, regardless of the type, because it can cause to machine to smell awful (I learned that the hard way with my Nacecare Henry).
As for vacuums in restaurants, that's something I'm not too sure on. The best thing I can think of for them is a central vac with an interceptor. I've seen lots of restaurants use push-sweepers, and those seem like decent options for picking up dry food particulate, then you could go back and vacuum up embedded dirt and steam clean/spot clean when needed.
As for carpets not being good in restaurants, I get your reasoning, but I feel like it can be done.