Phil, yep, I don't think it's that big a deal here at our latitude to worry about the number of brood boxes. They seem to do well in anything that keeps them safe. I don't know about building up in the spring, it works for me they have a lot of room...
I agree with Robo. Bees are from the tropics, and like us humans, they found a way to keep warm where it got cold enough it was dangerous to fly. It seems to me, a hypothesis of my own, that they found a way to protect their stores from enemies by building in a cavity. Then they built in a cooler place; getting out before the other species. In evolutionary science, that's called "Competition." The other, unless I'm just some old fart, favorite is adaptation.
Competition describes the species having problems with an opposing species for the same food or living space. It will force a species to change it's food source, or outdo the competing species for resources. In this case, we learned to build fire, sew clothing, and build tents so we could follow animals into places we usually wouldn't go.
With bees, they learned to build in a fortress. That gave them the chance to store and stay strong. But is also protected them from the weather and climate. A happy accident. This gave them the ability to build in a microclimate, one protected by the thickness outside the wood of a tree cavity, and stay in the climate of something on the winter weather of North Carolina, instead of the sub-zero temperatures of a Minnesota day.
I'm also guessing (Yes, doubters, just guessing. But with evidence...) the impulse to store, from the dry climate of Africa, they retain the impulse to fill every empty space with food for lean times. I'm reminded of a Jack London story about a starving sailor. When rescued, he would accept any bit of salt pork or hard tack. He would then hide it in odd places around his bunk.
My thinking is, they don't really need a lot of stores at our latitude. We have plenty of flying days, and when it's warm enough, they can go out and forage the Maples in January. But when the space is too cramped, they start doing funny things to compensate. They can't deal with extended cold spells. When it's warm they fill up the space and start swarming.
Mostly I'm thinking they just need room to expand in the spring. I have no problem overwintering a 5 frame nuc, but put a couple of supers on those 3 mediums, before the SHB gets to be a problem, and they knock themselves out to fill those empty frames with honey.