Relocatable Power Tap (Surge Protector TVSS) Question

While I was looking for a good metal case power strip (Which are very hard to find now a days) I came across the Belkin F9D1000-15 My question is what is the reason the label (That I posted a picture of) says "Do Not install this device if there is not at least 10 Meters (30 Feet) or more of wire between the electrical outlet and the electrical service panel" All my years of working with electronics & computers I have never seen that on a device before. Also does the 15 Foot power cord count in the equation?