Hate to be the bringer of bad news but I am seeing much miss-information going on here. The thing called O is several things.
First is the track. Ninety-nine percent of things running on rails called "O" out there are O-Gauge. According to
NMRA standards the width of the
standard O-scale track is 1.25" which is 5 scale feet not 4' 8.5". That is why the track is generally called O-Gauge even if the trains running on it are scale. The only O-scale trains that run on O-scale track (1.177") are what NMRA classifies as a
Fine Scale and calls
Proto:48. Lionel, MTH, Atlas, Rail King, Williams, K-Line, Marx, Weaver, and the old AHM regardless of 2 or three rail all run on O-gauge track. The only vendors (I know of) of true O-scale track are
American Switch and Signal and
Red Cliff Miniatures. 99% of people running on true O-scale track have hand laid it. The number of rails is irrelevant to the gauge.
There are differences in track for the more toyish trains such that have wheels with the deep flanges so they are easier to put on the track and can navigate tighter curves, and there for have to have taller rails. Generally the toy track is called
tinplate or
high rail track. This might be the better designation for us to use. Most -- not all -- non-battery powered High Rail trains also run on center third rail track to eliminate the reversing loop issues that plague 2 rail, and 3rd rail external type track layouts. Even using High Rail as a distinction to designate something as scale or gauge isn't really fair, because both HO and N ran on some pretty high rail as their standard for decades.
In the toy train world there are two major sizes of models. Standard O and O-27. Standard O follows fairly close to normal O-scale sizes of things. O-27 models are selectively compressed models to fit around O-27 curves. The 27 is the diameter of the circle. Standard O is also called O-31. Lionel also introduced larger sized curves for their more prototypical offerings first was "super O" which has a 72 inch diameter. In 1979 it introduced O-54 as a compromise between the standard O-31 and the unwieldy O-72. The issue at the time appears to be a new model of the Fairbanks Morris Trainmaster locomotive that wouldn't work on the O-31. Now a days there are more curve sizes than one can shake a stick at.
Having said all that, the issue of truck mounted versus body mounted couplers is an issue of prototypical correctness and a red herring as far as scale vs gauge designations. I mean look at N-scale. Mass quantities of N-scale equipment has truck mounted couplers. Until the Kadee Minitrains came out I dare say ALL N-scale equipment was truck mounted, but none would say that denies it the right to be called N-scale. HO has millions of units out there that have truck mounted couplers.
Coupler size - another red hearing. The unprototypical size of a coupler cannot be used as gauge as to whether something is called a scale or a gauge. The biggest example is the grossly oversized but ubiquitous Kadee #5. Probably used on 90% of the HO trains out there but still called HO-scale.
Finally in the O-gauge world the adherence to prototypical size is as varied as shades of green. Lionel had some amazingly correctly scaled equipment back in the 1950s. In contrast the import company Oriental made some really compromised (selectively compressed) brass models in that same time period. Now the Lionel company has many lines of products that range from the consumer mass markets junk to some really exquisite models that give a good showing against some brass models. This is no different than the various lines of HO scale equipment from Atlas, Athearn, Bachmann, Walthers. Same manufacturer totally different qualities of product.
The bottom line is we generalize and throw around terms where, when reading, we must be careful understand the context, and when writing be certain to clarify the context, or we are easily misunderstood.
I hated the non-prototypical look of the late 1960s and 1970s Lionel equipment, but when I got some I found it was sooo much fun to play with compared to my hard to wire HO stuff. Multiple trains, bells, whistles, fantastic track plans in a small space, all with just two wires to the rails.