"Is two rail supposed to be more "scale" perhaps?"
Oh, yeah, buddy. Even if not in size (most nice 3-rail equipment is 1:48, too), 2-rail is certainly far more accurate in wheels, track curve radius, couplers and, most importantly, track rail count: 2.
"Running tubular track would be why you can't run 2 rail cars."
The old-style Lionel round-top tubular usually gives the more (not completely, though) accurate 2-rail wheels fits, and I can only imagine a 2-rail car lost in a PW Lionel switch, even an 072 one - talk about a stranger in a strange land. Off in the weeds.
2-rail wheels do indeed typically - almost universally - smaller flanges, and the tread width is narrower, too. Both of these things can be a problem, especially in the switches, again.
Track with non-round rail heads (Atlas, GarGraves, Ross, Scaletrax, even Realtrax) will treat 2-rail wheels very well (GG track comes in a 2-rail version - same rail, minus one) - except for the switches, again. It's the deep Hi-rail flange ways intersecting with the skinny treads and skinny flanges - the wheel drops into the flange way and goes where it wants. 3-axle trucks can fake it, sometimes as 2 of the 3 axles are always on the track, supporting the other one in the flange way. Case by case.
Frame-mounted couplers, discussed above, are usually an issue. Blasted rules of geometry!
(BTW, GG and Ross have "tubular" rails, but they are not round on the top like PW Lionel rail. What little curve the rail has is actually pretty much like the real thing, which is not "flat-topped", either.)
