I thought OTG was just changing up where the host controller is sitting in the USB relationship? So you can have a device that acts like a client when hooked to a computer, or a master when hooked to a thumb drive/webcam/etc...?
AFAIK, according to the standard you still cannot use the B port as a host, it should instead be an AB port (a socket in which both A and B plugs fit).
I had an iRiver H320 with USB-OTG support. At the time I thought it was just a straight-up mini-B port but you're right, that's actually a mini-AB port!
Another example of mini-AB is the TI-84 series. Two calculators can be directly connected but a USB A-A cable is verboten by the spec (although I sometimes see them nonetheless), so TI put an AB port on the calculator and sold a mini-A to mini-B cable. It is somewhat confusing to users that a cable with two different ends was nonetheless completely transposable.
I'm not sure of this at all but I sort of doubt the TI-84 used spec compliant OTG, because in general the USB implementation on that calculator was very weird and unreliable and gave the feeling that they were doing something uncouth like bit-banging and not quite fast enough. I remember it routinely taking multiple attempts to get something to transfer successfully.
USB is a triumph of marketeers over engineers. All these things are called USB because USB sells (see also: Bluetooth).