I keep looking at the table on p42, looking at the footnote, and looking at the section right above it, and I keep coming to the same conclusion each time.
The footnote is relevant if and only if you're trying to set ad-hoc DCs for some wacky idea a character has come up with for a one-off trick. For skill challenges, I'd use the DCs straight, but if Leapin' Larry the Athletic Ranger wants to jump from the balcony, catch the chandelier and then do a triple backflip into the King's lap and give him a big ol' kiss on the lips.... THAT'S when the +5 comes into play.