[Ayatana] What are the advantages of an application-centric interface?

[Ed Lin <edlin280@xxxxxxxxx>]

In Unity applications and windows largely behave more like OS X while
the "classic" desktop is more like Windows.
There is a dock which represents applications as opposed to windows.
It focuses windows of a running application instead of launching a new
window and there is a single menubar per application, not per window.
This is what I call the application-centric interface.
I wonder why it was chosen as the preferred interface design because I
can only come up with reasons why the "old" window-centric model works
better:

Multiple Desktops:
The window-centric interface is a simpler mental model for the user as
it is more predictable. No matter what applications are running on
other workspaces or monitors a taskbar based interface will always
behave the same way. It's less noisy and disruptive because you never
get automatically switched to another workspace just because
coincidentally another instance of an application is already running
there. This particularly applies to such applications as file
managers, terminals and text editors that are opened frequently and
are used in different "work-flow contexts" say your "admin", "coding"
or "personal" workspace.

Window Management:
The taskbar requires one click to switch to any window in the current
desktop, in Unity switching to another window usually requires at
least two clicks.

Opening a new terminal/file manager window
Again, takes more clicks if launcher icon and active application icon
are the same. Keyboard shortcuts alleviate this for me but many people
never use those.

Menubar:
The menubar "outside" of windows is probably the most visible aspect
of the application-centric design. The main  problem here is that 3rd
party Linux applications are all written for the "classic" model. It's
not just LibreOffice and similar cases though. GIMP and Firefox
already have integration in Unity yet it's not perfect: If the toolbox
or download window is focused the menubar is empty and keyboard
shortcuts don't work. This is nothing that can't be solved as native
OS X applications show but my question here, is it worth it? Apart
from the netbook user case with maximized windows I can't see any
advantage of the global menubar. (If it was speed of access you
wouldn't have made hover only.)

My question to you: What are the reasons behind moving Ubuntu from a
window-centric to an application-centric interface? What are the
advantages and are they worth the trade-offs?

I want to like Unity, there is much to like about it, the launcher
keyboard shortcuts, the compiz integration, the dash, lenses and more
but please help me understand why app-centric should be better for me.