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. =)