I didn't get that from the CNBC slide show on this page. The amount of savings bonds has dropped some (from http://www.fms.treas.gov/bulletin/b2012_2.pdf page 41) but it remains nearly $200 billion.
I think this might just be a sign that it is now far easier to buy treasury bonds/bills/notes directly from the government without an intermediary which would fall into one of the other categories like mutual funds. Also after the 2008 crash more investors are in bonds having abandoned stocks.
I don't think medical insurance changes would have much effect on this. Medical insurance is like car insurance where annual income pretty well matches expenses plus profits with a little saved ahead for unexpectedly expensive years. They don't save much for the future like whole life insurance or annuity investments do.
The article stated that there are now four times the amount of companies included in this category which means that per company, investment in US Bonds has dropped significantly.
They have to keep adding additional types of companies to this category in order to get the same number.