I haven't seen an explanation for why cash isn't held in a regular savings account in the PP, but is instead held in the short term treasuries or money market accounts.  Why is that?

Craig, quick question about the Vanguard bond fund.  After looking at it's annual report, it looks like VUSTX (Vanguard Long Term Treasury) has only 84% of the fund in long term treasuries, whereas their VGLT (Long Term Government Bond ETF) has 93% in LTTs.  Is there another aspect to which one of t...