the objections to a dynamic system are logistic; the folks that manage the servers want to have a process where they take a tarball from A, copy it to B, untar it and walk away. The same process means that responsible people will be making sure the site goes through QA before being deployed to live, that writers won't be *capable* of breaking the live site, and nor will anyone on the outside be capable of hacking PHP vulnerabilities, throwing SQL injection into the db, or anything like that. The server admins don't even want a database on there.
graeme_p the strategy you describe is precisely what I'm after; in-house dynamic system and a static mirror on the live site. When I get some time to work on this (ie not today) the chore is assessing various CMS's and picking one that fits.
I don't expect the writers to do anything in SVN... that will be someone else's job. We'll let the writers fiddle with the offline site, then occasionally someone will pull all their changes into SVN for posterity and push them into the deployment process (dev->qa->staging->prod)