I have thought about this very thing for a while now.
Netscape and other browsers take note this is in my opinion
the failing point.
You are a web browser. Not an Email client. Not a news reader. Not X. Just do the web, please. You don't have to do everything to keep people interested.
IE has this seperated - of course like the article says they have a lot of programmers.
I would imagine a lot of effort is spent on those extra items and it distracts from the true task.