I have all three of these and absolutely none of them contain (or will contain at any point) a three phase motor. All three of these use variable speed motors in my house. I suspect even more will moving forward as well. So honestly three phase is pointless as I just need "power" to drive the variable speed controller system. My hottub has fixed speed 220 pumps but its old. I suspect newer systems would be moving to variable speed as well.
I think your pretty spot on that most people do not need 3 phase, even in the limited cases you mentioned. =)
If you have a variable speed well pump, it is very likely to contain a three-phase motor. What it doesn’t have is direct wiring from the motor windings to incoming power. It likely has a variable-frequency drive consisting of an AC/DC converter (for which there would be a small but nonzero benefit if the supply were three-phase supply) and three inverter outputs connected to the windings. And hopefully either the VFD is in or very close to the motor (Grundfos will sell you a VFD/motor/pump combo like this) or has proper filtering to reduce high harmonics and properly shielded wiring to the motor.
I think your pretty spot on that most people do not need 3 phase, even in the limited cases you mentioned. =)