http://www.census.gov/prod/2003pubs/p70-88.pdf
Thanks for sending that link, it's pretty interesting. I particularly took note of page 12 where it shows that the next group down -- age 55-65 -- has the highest non-house-equity-net-worth percentage, and page 13 that shows that for that group their retirement accounts almost equal their equity in their homes. The over 65 crowd is a little too old to have been able to take advantage of that; I bet we see the current 45-55 group in 10 years be dominated by retirement savings (especially when the real estate market cools off :).
and of course, we're already part of the way there: those are numbers from 2003.