In a spherical cow sense sure. But no one is buying the market return when they buy even a total market index fund. Other commenter is right, they are expecting past performance of these index funds to be indicative of future returns. But then again they aren't really actively investing either. Automatic contributions pervert a lot of the efficient market hypothesis ideas I think since these people are buying, routinely, maybe as long as they are alive, with no information in front of them.