Android XXHDPI resources
According to the post linked in the G+ resource:
The gorgeous screen on the Nexus 10 falls into the XHDPI density bucket. On tablets, Launcher uses icons from one density bucket up [0] to render them slightly larger. To ensure that your launcher icon (arguably your apps most important asset) is crisp you need to add a 144*144px icon in the drawable-xxhdpi or drawable-480dpi folder.
So it looks like the xxhdpi is set for 480dpi. According to that, tablets use the assets from one dpi bucket higher than the one they're in for the launcher. The Nexus 10 being in bucket xhdpi will pull the launcher icon from the xxhdpi.
Source
Also, was not aware that tablets take resources from the asset bucket above their level. Noted.
xxhdpi was not specified before but now new devices S4, HTC one are surely comes inside xxhdpi .These device dpi are around 440. I do not know exact limit for xxhdpi See how to develop android application for xxhdpi device Samsung S4 I know this is late answer but as thing had change since the question asked
Note Google Nexus 10 need to add a 144*144px icon in the drawable-xxhdpi or drawable-480dpi folder.