Without going into whether I agree with his assertions on Cocoa, if it seemed so much easier to do with web technologies, why didn't he just do it with web technologies?

Cocoa is probably the framework best suited for incorporating web views, and tons of apps do this: Mail.app, iTunes, Aperture, Colloquy, etc. etc. Use the right tool for the right job, if you have something that is going to have a lot of flow-based layout, then by all means use WebView.

It's kind of like refusing to use an NSTextView, then complaining about having to lay out text yourself.