Hey guys & gals, before you go off half-cocked, take a look at the specific architectures (there are multiple ARM target CPUs alone) and peripherals supported on tablets!! Android has to be ported by the manufacturers of each device! You can't go to Google, grab stock Android 4.1, say, and put it on your Android 2.3 phone, it doesn't work!!! You need specific device drivers, and the drivers have to be updated as well. Yes, they did port Linux to the Raspberry Pi, but there were literally thousands of people asking for it and hundreds of contributing developers, and it still took about 9 months from the release of the first RPi to get to the present Raspbian! (or Arch) and that was starting with a version of the Linux kernel and userland which was already written for the ARM processor core.
Ubuntu is going to try to get 12.04 on the Google Nexus tablet. That is a specific processor, specific peripherals, and a fairly large user audience. And you notice no Ubuntu 12.10 or 13.04 is mentioned. They hope to get it working prior to 14.04, is all. ARM versions aren't released every six months for ANYONE.