Think about this:

I'm a little guy … I pull in 100 unique visitors a day to my blog that occasionally writes a good article on WordPress. I make $50 every now and then when someone buys an ad on my blog (probably a premium theme vendor's ad). For me, it makes perfect sense to join a "network" or split profits with other WP bloggers. It's a promotion for me.

I'm a big guy … I pull in 1000-5000 unique visitors a day to my blog that writes DAILY articles on WordPress. I make $500-$3000 per month from advertising, affiliate marketing, or selling my own products. For me, it makes absolutely no sense to join a network, share my traffic, expertise, and income with a bunch of little guys.

A network or central blog might work. But it'll be comprised of little, mostly unsuccessful, small time bloggers looking to boost their profile, influence, or income, and it's probably something that nobody will ever read.

On the topic of the Codex:

Yes, the Codex is incomplete. Yes, we bloggers write a lot of content that could go on the codex. But, as someone mentioned, if we put it on our blog, we get the traffic, the recognition, and the income. Why would we ever give that up?

Generally, though, a lot of WordPress content published on blogs wouldn't go well on the Codex. It's personal writing. It's not a technical paper, it's a How-To article. The Codex is made up of function/template tag references with bare-bones explanations and examples. And that's probably how it should be.

Final thoughts:
If a WP user wants to learn about WordPress, you won't do well just studying the Codex. It probably won't work for you. You need to be proactive. Follow WP developers on Twitter. Subscribe to their blogs. Buy their products. Study their code. That's how I learned.