What happens in a specialty high-end mattress store has very little to do with the bulk of the market: people buying mattresses at Macy's or one of the numerous regional mattress chains. I don't have any experience in the super-high-end, but have worked with the low-middle-high end that you get going to a "mattress store". Those models are definitely not built-to-order, they're sitting in a warehouse waiting to be delivered, even the $4k+ ones that are trying to compete with the custom shops. For the bulk of mattresses the margins mentioned in the article are conservative.
What you're absolutely correct on, however, is that the cost of building a mattress doesn't represent the cost of running a mattress business.
However, that's exactly what makes it ripe for disruption: streamline the rest of the business model and loot the manufacturing margins.
Those mattresses sitting in a stack are bulk orders negotiated by the retailers. But you can still walk in and order something they don't have in a back room. Those are built and shipped. But that's not true for all mattress companies, just some.
What you're absolutely correct on, however, is that the cost of building a mattress doesn't represent the cost of running a mattress business.
However, that's exactly what makes it ripe for disruption: streamline the rest of the business model and loot the manufacturing margins.