So you are telling me that the Samsungs, and Sonys and Asuses of the world are forcing the navigation buttons to the left, despite the fact that they should be in the center?
Since Honeycomb, Android's "tablet UI" was such that there was no top notification bar, and the captive buttons (home, back, etc) were placed on the bottom bar to the left; and the clock, quick-access items and notifications were on the right. With ICS, Android merged the phone and tablet OS into one branch, however the UIs were still different in this regard.
When Jelly Bean was announced along with the release of the N7 tablet, the "hybrid UI" was introduced, as many called it. The UI on the tablet was more like that of the phone, with the notifications and quick-access menus on separate bar at the top, and the bottom icons centered since they were no longer sharing real estate with the notification bar. This same style persisted with the Nexus 10. Apparently there are still mods that can be applied to JB tablets that revert back to the old tablet UI, but it seems Google is trying to phase that out as it is no longer the default on the tablets it builds, though many Android tablet OEMs still use it with their custom UIs.