To be honest your request/demand expectation is quite unfair.
have you seen cross link on Suse and Red Hat and Ubuntu and SE Linux and Debian and... (well I would need a google search for adding more here)
By far I guess PostgreSQL community documentation is the one of the most organized doc stores (and the best dox when you need to see products limitation. No one else is so vocal). Only other better doc repository I have come across is MSDN. Well even there I can't recollect SQL server doc corss linking to SQL Azure.
Postgres-XC is a fork-serves different purpose, once it forked out it has nothing to do with PostgreSQL (to my knowledge the dev group as well is different).
Regards
Sameer
