I'd just like to know who makes this stuff up...

"Example of reading: a 23mm tyre can be safely mounted on traditional rims of 13mm to 16mm (internal width). On any rim wider than 16mm, it is not possible to use a 23mm tyre safely.

On the other hand, a rim that is 21mm wide internally, can only accept tyres from 35mm and above."

I've been running 28mm wide tires on 23mm internal width rims for like 2 years. And I've read on this very forum of guys running 700x23 on 21 and 23 wide wheels. And look at that, none of us are dead.