1. It has to be that way. It typically takes a designer 1 month to write 20,000 words for a 32-page chunk of a book. That means one author writing UC (256 pages) start to finish would take 8 months. We simply don't have the time in our schedule to do things at that kind of pace. Also, a single author writing 256 pages is going to cause burnout, which we don't want. Also, most authors would rather be paid more often than every 8 months. Also, most authors aren't good at or interested in all topics of a book, so splitting it with multiple authors allows them each to remain fresh and interested in their part of the book. Also, most designers work for other companies, too, and it's impossible to schedule an 8-month block of their time for a single project; as it is, I'm not always able to use all the authors I'd want for a book simply because they have a schedule conflict (for example, Brandon was working on Open Design's Midgard setting and didn't have time to work on Bestiary 3).
2. It's not the designer's *responsibility* to answer questions about the final book. They are welcome to provide feedback, especially in a "designer's intent" sense, but as the contents often change during development, sometimes their input can't resolve how the final rule is supposed to work. And remember that this is summertime and UC has only been out for two weeks, and many of the designers have been on vacation or at Gen Con, so they may not have been available for questions for a while.
As for rules questions remaining unanswered, that is what the FAQ is for, and I think we've done a good job in the past few weeks of clearing up new issues and started to make some real headway on the old, big issues like animal companions and grappling.
3. The AA/APG problem happened because the APG picked up the original text from AA, and the AA sold out so quickly that we had to quickly put together the errata... which happened right after it was too late to make changes to the APG. There was no miscommunication between Jason and I about brass knuckles, we've discussed it, and the update with appear in the next printing of the APG. Each book has a cycle, and sometimes one is updated more quickly than the other because of print runs and interference from other projects.