Mine say that too (40°C, a bit over body temperature, in case you are used to Fahrenheit). I wash them with 60°C though, which is the normal "near body clothing" washing temperature one should use.
Consumerist propaganda? I can't imagine many people taking it that seriously. I do, in fact, buy new underclothes every 2-3 months only because I prefer the unworn feel. I'm sure many would agree. Looks like a startup with a not-so-novel idea, but a nice ordering interface and hopefully nice ordering process that will succeed.