"Future development" means the release that will follow OpenACS 4.5, which will probably be some time in summer.
As to "why" it's pretty much the same reason as to why we no longer support PG 6.5.3 or PG 7.0 - the PG group doesn't support those versions, many bugs have been fixed that neither we nor they care to hear about any more, etc. There's not much reason to support something PG won't support.
Likewise OpenACS 4.5 will require Oracle 8i, not 7, while we don't yet support 9i.
Software rolls on and it's unreasonably complex to try to support an endless list of bersions no longer supported by the tool vendors themselves!
