I consider that a major upstream bug. Better would be for postgresql to ship a standalone SQL dumper, which can read old file formats.
Charlie,
Would you expect a "simple" upgrade of Oracle 10i to Oracle 11, for your major enterprise application? Or, MS-SQL 2005 to MS-SQL 2008?
Any major database version upgrade requires the attention of a qualified DBA who knows how to test data and applications against the new DB version, and then dump/upgrade/restore.
For example, PostgreSQL introduced some minor syntactical differences with 8.3. If your application uses the features affected by these changes, it would be impossible to simply 'dump/restore' without some massaging of the data and the application.
PostgreSQL does ship with a dumper, pg_dump. If you have the current version of postmaster, then you use pg_dump to connect to that and dump your data in a version-agnostic format. IMHO, the effort of writing a standalone dumper that can recognize all the old file formats is not worth it, because it is a mistake to delete the old version of postmaster off your system before you've done a dump of the database.
Cheers, -Josh