I have two installations of Ubuntu server 14.04.2 LTS, both installed from the same media (I just checked - the DVD used for both is still on the drive of one of them), but a couple of months apart. All packages appear to be up to date, but see the kernel version on one is higher than that on the other:
root@bud:~$ uname -r
3.13.0-55-generic
root@mud:~$ uname -r
3.16.0-40-generic
Why is this? Shouldn't I be running the 3.16 kernel on the first one?