While I don’t care enough to dig out my old 4e books, I want to point out that the rules compendium includes the rules as they stood in 2010 (when Essentials came out). There was a ton of errata before that point (and I mean a ton – sometimes it seemed 4e was doing errata in real-time).
Skill challenges were almost certainly one of those areas affected, considering they were revised for the – I wanna say – DMG 2.
The big change was before it was 9 successes before 9/2 failures, and after it was 9 successes before 3 failures.
And the DCs where tweaked.
The core part of skill challenges was really simple:
A check moves you towards success or failure by a measured amount.
As a DM, for a complexity X challenge, you can ask for 2X+1 successes before you should shut up and let the PCs succeed at the stakes in question.
At launch, after X failures you also shut up and let the PCs fail.
After revision, after 3 failures you also shut up and let the PCs fail.
You decide "how complex is this problem", and then this gives you a budget for how many hoops you are allowed to put the PCs through. If you ask a PC every round to make a stealth check? Well, there goes your complexity budget.
A failed stealth check, is everything over? Do you give the PCs more chances? Well, count failures! Keep giving PCs more chances until you run out of failures in your challenge.
So a PC sneaks into a castle to get the plans for the winter's ball (where they want to assassinate the king).
If you ask for 10 checks and the PC passes 9 of them, you just blew your skill challenge budget for a C4 challenge. If it is C5, you can ask for 2 more checks, if they both succeed, the PCs succeed at the challenge.
When the PC fails a stealth check, does everything fall apart and the challenge becomes impossible? No! You need 5 (at launch) or 3 (after revision) before you get to say "your plans aren't going to work" or whatever.
So, how important is that sneaking? Only a bit? Well, give them one stealth roll. On a success, they manage to get the plans. On a failure, they get part of them, and alert the guard that something is up on the way out.
Something more important? More checks and detail. Something less important? Call for one check, and narrate results in bulk. Something irrelevant? It doesn't work, no check. They do something stupid that pretty certainly makes things harder? Here, have a failure.
Much like the encounter building rules of 4e, they are a tool to build an encounter.