I suspect a lot of people become expert in a "CMS" like WordPress or Drupal, because it seems easier than learning to work with a proper framework like Rails, and then find themselves stuck inside the platform.

Like project management systems, CMS is destined to be reinvented by everyone, every day of the week.

It's very hard to convince people of going with a proprietary, custom solution. Many people have been burnt here, and it's a tough sell to upper management.

All CMS is necessarily a "proprietary, custom solution". All CMS (like all software) exists somewhere on the spectrum of "easy to use" vs "extensible and customizable".

If management chooses to rely on a vendor to set the roadmap, then they are fools, and there's not much you can do to help foolish management.

Here's another vote for SilverStripe. I've run it in production for a year and a half and been very happy with it's performance and caching options. (You can do partial caching all the way up to a full but automated static export.) The MVC framework borrows a bit from rails and makes it one of the nicest PHP CMSes to develop for. It's much more fun than managing WP custom post types and the interfaces I can create for end users are better. Downsides? Documentation could be better and not as many off-the-shelf modules available. Both LibreOffice.org and OpenStack.org are powered by SilverStripe.

I agree SilverStripe is really clean to theme and extend... however some of its base functionality can be a little dodgy at times :)

Still the best open source CMS I have used.