Now the Gmail's mobile app and the mobile site look almost the same. The new web interface can be accessed from iOS, Android, BlackBerry and Kindle Fire but on Windows Phone, Gmail.com still looks ugly.
New interface vs the old interface in iOS and Android:
IE10 in Windows Phone with (right image) with a horrible outdated design of Gmail.
It's not like IE10 in Windows Phone can't display the new interface. Google is playing a game here. May be an answer to the Microsoft's Scroogled campaign...