How long is supported every release?

How long is supported every release?

As long as (K)ubuntu, because Ubuntu repositories are updated as long as they support each version.
That means that Kubuntu decides when and how many updates they do for each version.
For example Netrunner 4.2 (Precise) LTS and 12.12 (Quantal) with the kubuntu-backports-ppa enabled, can currently be updated to KDE 4.10:
http://www.kubuntu.org/news/kde-sc-4.10
If Kubuntu backports KDE 4.11 for Quantal and Precise, so can Netrunner update.