Predicted lifespan of different PostgreSQL branches

I spend some time googling this and searching the Postgresql.org site, but
I'm either not good enough with the search strings, or it's not to be found.

I'm trying to plan upgrades so that we don't upgrade needlessly, but also
don't get caught using stuff that nobody's supporting any more.
The FreeBSD project keeps this schedule:
http://www.freebsd.org/security/#adv
which is _really_ nice when talking to managers and similar people about
when upgrades need to be scheduled.

Does the PostgreSQL project have any similar policy about EoLs? Even just
a simple statement like, "it is our goal to support major branches for 2
years after release" or some such?

--
Bill Moran
Collaborative Fusion Inc.