The Satyr's Pipes from SS aren't normal magic items, they just enable the Satyr's racial ability. They only function for Satyrs, and they don't use the standard Save DC for a magic item.
Sleep, Fear, and Charm Person are all 1st level spells, and would thus have a DC 11 Will Save, according to the normal rules. Instead they have a DC 14 Will Save, which doesn't match any of the normal formulas. (The Satyr has 5HD and a Charisma of 13. The 10+1/2 HD+Cha modifier formula only gives a DC 13, not 14.)
If you really want them to increase the DC, create a "Pipe Focus" feat that gives it a +2 DC.