Calculators like those are figuring that the next 40-50 years will be as prosperous as the last 50. I do not have faith that stocks will give a 7-8% return in the coming years. If you believe that crap is going to hit the fan, that this depression will continue, or that America is in the beginning stages of decline, then there is a good chance you will lose money.
My wife's employer just offered her a matching 401k. She said thanks, but no thanks. I took the tax hit and closed out my Roth IRA late 2007. Personally, I am done with all those investment shenanigans.