Android so far has been maintaining its separate kernel from the mainline Linux kernel. The android kernel forked out of the mainline because of differences in accepting the changes which the android developers were working on.
The good news is now with Kernel 3.3 the android specific changes are accepted in the mainline kernel.
Ubuntu 12.04 scheduled to release next month, will be on Linux kernel 3.2, expect 12.10 to benefit from this.