OK, Gmail is the best Webmail service out there, but this proclamation is just a bit premature. Offline access is only a few days old and "experimental" (what does that even mean inside a service that's still marked beta?). also, Outlook is just a client - you have to get email service somewhere else - so Gmail doesn't need to destroy it.
I have been playing with this since it showed up in my preferences yesterday morning. Quite impressive. I already use GMail almost exclusively. Now I can transition completely and do so without the worry of connectivity. :-) (If only they would get on the ball and release a Mac OS version of Chrome with which I can experiment.