@atmasphere --
This statement is false. If you encounter a standing wave, it often cannot be fixed with only 2 subs. And it can't be fixed with room correction or room treatment.
Now if you **don't** encounter a standing wave then its all good. But in many rooms a standing wave is highly likely- unless the room is irregular in some way. But any rectangular room will have a standing wave which will be a different locations throughout the room depending on the frequency. In such cases while that bass might be good at the listening chair for certain pieces of music, it may not for others. This is a simple fact of physics.
With a distributed bass array this problem is solved.
There's nothing categorically false with poster
@rauliruegas statement; you CAN have bass that is accurate, detailed, smooth, natural and effortless with two subs, end of story. Both room correction and -treatment can do wonders here, I find, and can (and should) be used sparingly for a successful outcome. Honestly it's becoming trite hearing the constant babbling about what a pair of subs can't, and the double count can. We know by now - 4 subs can be a hoot, and they ease up on the need for PEQ, definitely not trivial. Moreover, all things being equal a double-up in sub count gives a theoretical 6dB's more headroom, and I can certainly vouch for the importance of that.
You could however take a pair (or more) of bigger, more sensitive subs placed symmetrically to the main speakers, horn load them even, and have a different kind of awesome with other advantages. I know, size is banned in audiophilia, but the simply fact of physics, to use your own words, also has size as a main priority that numbers can't alleviate. Big subs in high numbers, however..
And what's the issue and argument made with smooth bass coverage over a wider listening (position) window? One sub is a narrow sweet-spot, two is wider and so forth, and while a single sub may boarder on the head-in-a-vise sweet-spot, two is definitely good for a pair of listeners to have decent coverage. I don't know about you guys or ladies, but mostly I tend to listen to my setup by myself (and if not I give the other listener the sweet-spot, usually placing myself on a chair behind and to the side of the listening sofa), and I don't need for bass to be swell in every goddamn place in the listening room; the listening position (with room for two, if need be) will do just fine, thanks. Actually this is mostly dictated by the main speakers; I would never listen seriously any other place than smack in the middle between the mains, but that's just me.