- The OS/desktop manager-specific stuff needs to be there, or else you fragment the overall UX for the computer.
- The browser needs to give immediate access to the actions that a typical user will use all the time.
- Tab mode has won out over separate windows, so you need a visual indicator of what tabs are open and which one is active.
- And the contents of the web page are the contents that you care about right now, or else you're looking for a way to navigate away.
Modern browsers do a pretty good job with all of those requirements. I'm surprised that Bray is even interested in a notional "home" page, since everyone I know, technical or not, either wants their session restored from last time (on startup) or a very fast search page to come up when they tap for a new tab. People don't reset tabs -- they close them or go somewhere in specific.
Best of all, this behavior is all customizable by normal people who never have to type about:config.