The base of the operating system, Debian, comes in three versions: Stable, Testing and Unstable. Normally, Ubuntu is based on Testing; the LTS releases are based on Stable.
That cannot be true then for 12.04 because Debian Stable (Squeeze) is almost going to be old-stable, and it's obvious that the kernel versions in 12.04, packages, etc. cannot have come from Debian Squeeze.
So then what other Debian Stable is there for Precise to be based on?