They might conclude the same thing if they only looked at my 401K contribution, since it's less than half of my total monthly retirement savings. I wonder how many of their participants are also contributing to a Roth or traditional IRA, or to taxable savings accounts? Surely the outlook would be at least marginally rosier, no?
My company has a very generous 401k match, but limits my selection of investments such that I find it unappealing to contribute non-matched funds. Instead I contribute to a Roth and a taxable account, where my returns have been much higher than my 401k returns. I would wager many of the study participants who are paying attention to their retirement accounts are in the same boat.