Short term bond funds would be expected to provide a higher return because they add more risk(liquidity risk, interest rate risk, default risk), as opposed to 'risk free' cash.
Also, notice I said bond funds, not bonds.
For example, currentle the Vangaurd Prime MMF yeilds 4.28%, and the Short Term Bond Fund Index yeilds 4.77%.
http://flagship5.vanguard.com/VGApp/hnw/FundsByType
-Matt
For a longer explanation goodle bond/risk or something.