They've got an ingenious model from a profit perspective as well. Since you can't charge subscriptions for stuff like that, they can sell you pieces of a Sactional and then you can get more pieces as the space you live in gets bigger or your life style changes. They also sell additional covers so if you get bored of the previous ones, you can change the color without getting a new couch (though it is not easy to get them on and off).
My advice, wait until it's on sale. They regularly go for sale from 15-20%. If you aren't fussy about the type, Costco usually has them too.