I'm not buying the "you have to be an expert for a skill to be useful" argument. In the game I'm running, I can ask for common skill checks like Insight, Perception, Athletics from anyone. And it's not unusual when the rogue tries to calm down an agitated bystander that I ask for a diplomacy check, or when the warlord says he's with the city guard, that I ask for a bluff check. Few sessions ago, I asked the shaman trying to jam a portcullis to make a thievery check, and I asked the wizard trying to cross a thin ledge in some ruins to make an acrobatics check. I use Endurance checks as part of skill challenges sometimes, that everyone has to make, and if half the party or more succeed, they get a success and do whatever they are trying to do in less time.
Skills are not just for the specialists to "win" a skill challenge. They are used frequently enough during adventuring by everyone, so Jack of All Trades is a reasonably good feat for anyone who wants to be better at those skill checks, or to be a helpful assistant in skill challenges. Also not all parties can cover every knowledge skill so having a bunch of +2's on knowledge skills is also great, especially with strong Int/Wis like an Avenger who is not traditionally a knowledge character.