Migration Between Releases

Could someone clarify the database dump/restore requirement for postgres
upgrades between major releases?

The online help chapter "23.5. Migration Between Releases" states that:

As a general rule, the internal data storage format is subject to change
between major releases of PostgreSQL (where the number after the first dot
changes). This does not apply to different minor releases under the same
major release (where the number after the second dot changes); these always
have compatible storage formats. For example, releases 7.2.1, 7.3.2, and 7.4
are not compatible, whereas 7.2.1 and 7.2.2 are.

I thought that the major release was the first number in the versioning
schema, the second represented minor release, and the third would be the
maintenance release or revision number (i.e. 8.2.4). I need to understand
this better for the sake of writing install scripts for my own Solaris
packages. Originally, my scripts were checking for the difference in the
major release between the output of "postgres -version" and PG_VERSION file,
looking at the first module of the versioning schema (i.e. 8 in "8.2.4").
Is this still true, or should I be checking the minor release as well?

Thanks in advance,

~george