Other than Math, there are no posts that show WotC confirmed it. I find that claim dubious.
No, the whole skill challenge system is really messed up. I just can't make sense of how it's supposed to work.
There's two ways players can go about it.
1) They are all making their own skill checks:
If it's based on skills that the players aren't strong in then they have a low chance of success, and if it's based on skills that they are strong then their chance for success actually improves as the complexity goes up. The result is more XP for an easier challenge.
2) They are all using Aid Another to help the one player with a high skill relivent to the challenge:
Aid Another is too easy and it always succeeds after level 21. YOU CANNOT FAIL IT from 21 onwards because all your skills are at least 10. So the player with the strong skill gets a big plus and almost always succeeds....and again, the higher the complexity the more likely the players are to succeed.
I've made up my own house rules for Skill Challenges, and so far they've worked well:
During Skill Challenges the DC of Aid another is 10+half level, and a failed attempt results in a -2 penatly for the person you're trying to aid.
The Complexity for long Skill Challenges is always 3, and the DC is 15+half level. The Complexity for short Skill Challenges is always 1, and the DC is 13+half level.
If you want to increase of decrease the difficulty of the challenge, increase or decrease the DC. 1 point either way is worth 2 levels.
With the skills my players have they have a 70% chance of success on long challenges (gaining XP for 3 standard monsters) and an 80% chance of success for short challenges (gaining XP for 1 standard monster). Considering how easy it is to kill 1 to 3 standard monsters, it seems fair.