Which is why a gamer isn't going to be able to provide good feedback on the core design of a game. If they are, then they're basically no different than the designers.
By that logic writers don't need beta readers or editors. But whatever.
Editors fix errors in books. Readers don't. Wizards has editors and beta testers. What do you think all these organized play events are about?
And gamers play games and find where the designers' ideas fail in actual play. And judging from all the eratta, bugs, power gaming loopholes, errors, etc they need new beta testers and editors. Maybe people who are more experienced playing games who can catch the silliness all these so-called pros missed. Hmm, hauntingly familiar. Kinda like WotC and Paizo having great big open playtests. Glad the so-called pros can see this need, even if you can't.
Editors fix errors in books. Readers don't.
I don't know if I agree that it is the main reason, but I think you're right that it's a factor. (You're certainly right that the 4e adventures are, on the whole, not very good - although I think some of WotC's 3E ones were pretty weak also.)the terrible quality of adventures for D&D4 is the main reason for the edition war in my opinion
I have mixed views about Monte Cook. Some of his Rolemaster work was good, but not all of it was. 3E has some clever stuff in it, but some clunky stuff as well. I think AU/AE shows some pretty interesting ideas and design - I'd like to see the 4e version! But I get a bit of a vibe from L&L that Monte is not much into 4e.Am I the only one who thought this was a Pros/Cons of having Monte Cook on the design team, which I imagined would be followed up by an unqualified scale from 1-5? That would have been funny.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.