No, you're taking a rule from the COMBAT chapter where there is an action, Aid Another, and applying it to a non-combat situation, a skill challenge. Actions apply to combat only.
So you are claiming that Aid Another can only be done in combat?
I can Aid Another someone else to pick a lock in combat, but not out of combat?
Teleportation is in the combat section. Do the line of sight and line of effect rules not apply out of combat as well as in combat? Or are you claiming that teleportation cannot be done out of combat?
Your position here is totally unsupportable.
We've been using the term "Aid Another" as a convenient tag for this mechanism but more properly it is covered in the skill chapter in the topic "Cooperation". This topic clearly states that "In some situations" one PC can cooperate with another to provide a skill bonus. Its not a mechanism that PCs are universally entitled to. A player CANNOT assume that cooperation is always available.
The phrase "in some situations" is vague and not a rule. It could mean anything. It could mean, like you claim, when the DM allows it. It could mean when the PCs are standing next to each other. It could mean anything. You cannot use a vague phrase to force a given interpretation.
This is called inference. You are inferring something from a sentence where the sentence is vague and not explict.
Sorry, that's not a rule.
In non Group Skill Check situations the DM is perfectly within his or her rights to simply state that any characters using a skill need to make their own checks and that those checks count for success or failure. I don't even see how that fails to model cooperation in most cases. It just doesn't make the challenge easy cheesy and likely motivates unskilled PCs to try something different. Honestly how helpful is a fighter with no specialized knowledge of Arcana going to be to the wizard who is a master of Arcane knowledge?
Happens every day in real life. Someone not knowledgeable about cars says "What if you clean out the carburetor?" and even though the car does not even have a carburetor, it triggers a thought in the mind of the auto expert to clean out something else.
It gives the expert a bonus.
If I were working on a set of partial differential equations do you think the janitor is going to be helpful? (OK, maybe if he's the MIT janitor

). If the PCs are all trying to climb a cliff, sure, but that's the exact kind of situation where a GSC is appropriate.
The whole point of discussing secondary skills was only to point out that any mechanism that lets a PC participate which isn't better than just using "Aid Another" might as well not exist if you assume you can always AA. The very existence of such things suggests that AA was not envisaged as being an option that was always available.
Secondary skills have nothing to do with gaining a +2 bonus. Quote the rule.
There are two bonuses possible in the skill check section of the rules.
1) DM's Friend in the Running a Skill Challenge section.
2) +2 in the Group Skill check section.
Your logic is flawed. A DM could allow both #1 and #2 here. They are not mutually exclusive like via your theory.
Both are allowed. The update clearly indicates that not only is the second one allowed for non-group skill skill challenges, but that there is even a limit of one or two of them.
On checks that aren’t described as group checks, consider limiting the number of characters who can assist another character’s skill check to one or two.
This does not state: consider limiting the number to zero. It states, consider limiting the number to one or two. For your interpretation to even be close to valid, the update would have to have the DM limit assistance to zero to disallow assistance. Sure, the DM can do whatever he wants and ignore this rule, but this is the rule. You have no counter rule to it.
Yes, via the rules, the players are ENTITLED to use group skill check limited to a max of one or two in a skill challenge. And yes, the DM can overrule that for certain circumstances.
It cannot be used where the PCs cannot cooperate. For example, chasing a Thief down an alleyway and using Acrobatics to get over a wall cannot use the assist if the PC ally is far away. He can typically (unless the DM is a rat bastard) use the assist if the PC ally is next to the wall (i.e. he gives the other PC a boost).
The DM is final arbitrator of this, but the general rule still stands. Group Skill is allowed in skill challenges, even if the skill is not considered a Group Skill skill. The update clearly spells this out.
See, this is the problem with your supposition about AA, the rest of the SC system simply makes no sense when you assume anyone can AA at any time in any challenge. Either its at the DMs discretion or the whole SC system is mostly nonsensical. Criticizing it on the basis of a rules interpretation that breaks it is well sort of just itself kinda nonsensical when you can simply not interpret the rules that way.
It is at the DMs discretion. Every aspect of the game is. If I say something stupid in a skill challenge and rolled a 20 on the dice for Diplomacy, the DM can still call that a failure.
Your entire POV hinges on a +2 example for a secondary skill that is explained via the DM's Friend text. However, secondary skills have nothing to do with this conversation. They don't give +2 bonuses. You have no explicit rules to support your POV and hence, nobody else can be expected to intuit that POV from the rules. This is called interpretation (and a very off the wall one at that), but it is not rules.
And for the rest of this discussion, I will not use the term Aid Another. It really is that, but I'll use the term Group Skill.