This kind of reasoning on the part of DHH is troubling to me. He's basically saying that there is always one best way to do something. That may be correct. But what's troubling is that Rails is so focused on its "One best way" to do everything. Rails forgoes complete through-and-through consistency in favor of "magic" -- because it's quicker and easier. That's fine, but it doesn't have the ring of complete truth that I expect from a truly great idea, or framework.
To be fair, a big part of the Rails 3 rewrite was making it modular so you could have different opinions. Of course, not everybody was as equal as everybody else; a lot of Rails extensions seem to assume that you stuck with the defaults. Devise, last time I checked, was very hard to integrate if you switched out ActiveRecord for Sequel. But my information is a couple years out of date.
I think this blog post is really more about reminding people of DHH's brand than adding anything new. Rails has always been "opinionated" software.
