Buildings aren't "pre-built" (it was taken out of context I think), you still have to build them yourself, it's just that with humans and elves they are restricted to build plots within the village/town/stronghold radius. You still start from "scratch".
It wasn't really said how many upgrades there will be. Those "few" mentioned refer to upgrades for buildings (something like barracks lvl1 -> barracks lvl2) I think. Nevertheless, I wouldn't want masses of upgrades just for the sake of having upgrades. I'd rather have 5 meaningful upgrades than hundreds of those armor lvl1 -> armor lvl2 -> armor lvl3 etc. types.
And the building location restriction isn't so severe because you can still use army camps to secure remote locations and create forward bases for unit production which is the only thing that really matters. You'd want your economy and "tech" buildings to remain behind walls anyway.
Plus this only applies to humans and elves, others seam to have quite different systems and I for one welcome the diversity.