Ubuntu – Does Canonical provide paid support for individuals

To address your main question directly, yes, a later version in that release should remain supported. Now, for a bit of background, support for displaying the information to which you refer was added in:

synaptic (0.63ubuntu3) lucid; urgency=low
[..]
  * debian/patches/10_ubuntu_maintenance_gui.dpatch:
    - updated to support LTS and new "Supported" flags 

 -- Michael Vogt <michael.vogt@ubuntu.com>  Mon, 25 Jan 2010 09:58:35 +0100

This seems to be a server override issue instead of a Synaptic issue.

Let's look at the override information for linux-headers-2.6.32-21-generic and linux-headers-2.6.32-24-generic at http://archive.ubuntu.com/ubuntu/indices/override.lucid-proposed.extra.main.

The former is:

linux-headers-2.6.32-21-generic/amd64   Supported   5y

and the latter is:

linux-headers-2.6.32-24-generic/amd64   Supported   18m

For what it's worth, this inconsistency is resolved for subsequent Ubuntu releases.

The best information I have been able to find about the program is this. It seems to spell out in detail the level of service as well as the response times you can expect for varying levels of severity. Certified hardware is of course better supported.

Hopefully someone with personal experience can provide you with a better answer.