This is explained in the release notes for Precise:
By default, the 12.04.2 point release will ship with a newer 3.5.0-23.35 Ubuntu kernel from Quantal, and a matching X.org stack. This is based on the 184.108.40.206 Extended Upstream Stable Kernel Release...The purpose of providing a newer kernel in the 12.04.2 point release is for hardware enablement.
This only applies to Ubuntu, Edubuntu, and Mythbuntu.
In short, you get the newer kernel if you install from
12.04.02; but keep the older kernel if you update
12.04.01, unless you take steps to enable the update.
For more information on how to do that and various policies and procedures on this issue, see LTS Enablement Stacks.
The support schedule for the kernels is given at the Version Matrix