disk format changes

Hello to Everyone,

First, I'm new to postgres and fairly new to Linux (redhat).  Really
love what I've seen of postgres, and this list so far.  It is
obvious there is a lot of experience on this list.

In the weeks I've been following this list I've only seen one
reference to my question, and I wasn't able find anything in the
docs.

Why does the on disk format of postgres change between major (not
sure if that's the right terminology) releases?  Benefits?
Drawbacks?

As someone new to the "scene" the thought of "dumping" databases,
running initdb, then restoring the databases is... umm... (looking
for the right word)... daunting/scary/silly.  Especially for
production dbs.

However, I've also noticed that many on this list are running some
"serious" postgres installations and this apparently isn't a
concern, so I thought I'd ask.

Thanks!
Craig
craig@dashsystems.com