How often do you need to replace foam? Our 10 years + 2 moves old couch (that cost iirc $700-800 then) is basically good as new. I guess we don't have kids or dogs, the worst thing that happened to it is a gerbil briefly finding a way into the hollows :)
Removable cushions in a couch are pretty rare.
As a counter example, both of my couches still have perfect cushions. One bought for C$800 15 years ago and another for C$1500 5 years ago.
But for the couch, is it unreasonable to want a couch in which I can replace the foam? For not wanting a throw away product?