Also, some people I know stick to old versions for (closed source or
inhouse developed) software that is hard/impossible to port forward, or
just random inconsistencies between versions (automount troubles between
CentOS 5, CentOS 4, Fedora 8 and 9 here were a recent example; we are
working on open source related to the ALMA radioastronomy observatory,
there they are still running ancient Red Hat Enterprise Linux versions due
to software written in "C++" as understood by old GCC, newer GCCs just barf
at the code and rewriting/retesting that huge mess is a titanic job just
now really underway).
On philosophical grounds, I'm against forcing people forward, even for
their own good... /encouraging/ them forward is a much better idea.