Thanks for the praise - glad to be able to help. As a known rules master like DracoSuave has made a post without commentary, I can only hope my example is considered to be correct!
As a further commentary, I find 4E's skills and how DCs are based on passive checks makes for a very either-or like situation.
Either you're trained in the skill (like Stealth, or Bluff or whatever) coupled with a good ability modifier for that skill and then you do the sneaking or bluffing.
Or you're not trained and have a 10 in the ability. And then you don't do any sneaking or bluffing.
The difference can easily be 10 or more.
This makes the PCs that do sneak only fail on a 1 or 2 against reasonable monsters of their level. If two PCs do the sneaking, the risk of being detected is only 5% and 10% (or 14.5% altogether).
As the risk of detection for two PCs of the other category is 80% (assuming individual failure rates of 50% and 60%), that simply does not happen. They will solve their problems another way.
So beating a passive DC is very much an either-or scenario. Either you're trained for it, and then it's hardly a challenge; or you aren't, and the chances of failure are so overwhelming that it isn't even worth a try.
Just saying. I know I would have liked to hear this three months ago, so I didn't have to wonder if there was something wrong with the rules...
Beating passive DCs is in practice very easy (if it isn't, you don't even try).
In this I find D&D lacking, to be honest. Makes me long back to percentage-based skill games, where the "trained" character might have a 60% score while the completely untrained one has 30%.
Or at least, D&D is lacking in the way that it can be rather difficult to assemble a team with no weak links, so that skill use becomes a truly viable way to accomplish your goals. (Any party where everyone is trained in Stealth with at least a secondary Dex skill will have trouble filling out all combat roles; as will a party where everyone combines Bluff training with a good Wisdom.)
The difference to combat is stark - in D&D the only area of competence you can be sure everyone is trained for is combat. No wonder many players give up and resort to solving all their problems by bashing heads in!