Mattress Buying Is Very Annoying

I agree with Rohin Dhar that the mattress industry is rotten. However, not because of this:

The top four companies (Sealy, Serta, Simmons, and Tempur-Pedic) make up 59% of the industry revenue. The top fifteen mattress companies make up a whopping 81% of the market. Low levels of competition lead to consumers paying obscenely high prices for mattresses.

Is this unusual? It doesn't sound all that unusual to me. Four companies that control about half the market and a dozen that control 80% of the market? I don't know what's average for national industries like this (or even how you'd calculate "average"), but isn't this pretty average sounding?

(Via Andrew Sullivan.)