Reducing the supply of UST !=Increasing the money supply. All QE is doing is increasing bank reserves. Unless bank lend the reserves out money supply is not affected. With IOERR and general aggregate demand being jacked, banks are not really lending money out to actually increase the money supply. If just taking UST's out would have increased money supply we would have seen a lot more inflation!
*edit: IOER = Interest on excess reserves. See http://synthenomics.blogspot.com/2012/08/interest-on-excess-... for a good explanation