Ubuntu is just one of many "flavors" of Linux. Linux is what the Android OS is based on. Linux itself is a variant of Unix, and there are other offshoots from that as well (such as FreeBSD, which we use on our dedicated hosting server). Embedded Linux will become prevalent in the coming years, but not Ubuntu...I personally had too many problems with it on multiple computers, and support was/is poor, so it is not even on our radar anymore.