I have read with great interest this discussion relative to web applications.
Now I'm facing a very similar problem with respect to notification/status information inside Desktop applications. There are some design guidelines from Microsoft here describes the role of notifications, giving clear distinction wheter to use a "growl" (notification are baloon) or a status bar, but they do not explain why they are built the way they are and positioned where they are (bottom).
I guess one answer is "tradition": it is a common element of the classic Windows UI.
On the other end, web applications always display "status" and notifications at the top: this site, twitter/facebook, ... Google documents display some status information, things yuo find in the status bar usually, in the empty space at the right of the menu bar.
And even in Windows recently I have seen something different from Visual Studio with Notifications
The notification icon is inside the title bar, at the top.
Why status in desktop is at the bottom, in web at the top?
The only answer I found, but I have no idea if it is supported by studies/facts, is that this might be due to the fact that the web is "bottom - less": a web app/page very often has a top, but a very "vague" bottom. Is a scrolling page more than a square window. So: no bottom - no status bar at the bootom.
Is this a valid reason? Are there any other, more compelling?