Usability is not the issue. I would say that drawers are removed more times by the installer than by the end user. And which way the lever is pushed has no effect on normal drawer operation.
I always thought if if the/a lever does not work in one direction, try the other. I'm betting three way switches really throw a wrench in the works. You know the ones that up is some times on and sometimes off, depending on the other switch position. LOL
And FWIW if the lever on both sides went in the same direction it would mean design changes, and the installer having to keep up with which slide goes on which side so that you would not end up with some drawer slides that get mounted up side down where some drawers require both lever to be pushed up and some pushed down. And every manufacturer would need to take that path. Symmetrical Push Buttons on these type slides did not last long, and they were essentially the answer to John's dilemma. Most slides have improved/progressed to this point. There would be more compromises if the slides were dumbed down.
It absolutely would require more attention on each and every installer to insure the slides did not get installed up side down and it would not guarantee that would happen. And if it happened you would be right back in the same place.
And yes he has a good point for those that need to be shown how to do everything.
It is a situation of way over thinking a solution to something that is not a considered to be a problem. If only there was a simpler way to "read" a book with out having to learn to read.