Personally, I do not want to see a sidebar, taking up a third of the screen, on my smartphone. I find the example that he considers fine quite unusable and would not read that on a smartphone.
The issue isn't, I think, responsive design itself, it's that it's not so trivial to make it work better than device-based workarounds.
Edit: I don't mean to say that it's necessarily a bad idea to go responsive -- it's just that it's not a clear, universal win.
This is one of the main reasons I love readers like Instapaper.
No.
The sidebar works and is effective when there's significant horizontal space, such as on a desktop screen with ample horizontal space. It just does not work when horizontal space is a premium, as is the case on smartphones (which generally barely fit a standard typographic line length at readable size in portrait)
This is a really weird argument; sidebars are preferable to a lot of other patterns depending on the site and doesn't at all mean the content is less important than anything else on the page.
No, it's pretty much on target. Sidebars need to go away.
Obviously, if the sidebar does not add much (like on many blogs), I wouldn't mind if it goes away entirely.
edit: Columns seem to be problematic when there is no well-defined "end-of-page", as on paper.