Doesn't quite feel right to me, but, whatever, I make my own DC's anyway.
For skill challenges where I'm tracking success and for group checks, my hard DC's are likely to be lower than these. But for other various skill use for knowledge checks and the like, I might use the higher hard DC's when the consequences of failure aren't so bad, or when I'm not tracking successes, but simply running a gauntlet.
Tangent: The other day we were discussing in our group what would be the DC for swinging yourself onto a running horse as it runs by you Legolas style. We had some very different opinions on this. One person said DC 25 or 30 because it's not something low level characters should be able to do, but high level characters can. This is not the 4e way though, you're supposed to just assign a difficulty to the stunt, and anyone can do it. I was saying in my game the DC would be between easy and medium difficulty, if I required a check for it at all. The way D&D combat works, a running horse double moves 20 squares, then stands around while everyone takes their turns, and then double moves another 20 squares. During that time it's "stopped".
Back on topic, setting skill DC's is more art than science. You pretty much can manipulate the math to get the end result you want, especially when you know your party. It's just one of many knobs and dials in the system to design what you need, set a pace or difficulty, or challenge one or all members of a party.