[katzgrau]

There are a lot of companies with a proprietary CMS in the general publishing space (TownNews, GTXcel are both popular), but you can bet that their customers and prospects are always considering a switch to WordPress for various reasons. Financial, extensibility, the fact that most people just know how to use it, not being tied into a 3 year contract, feature list, great reputation, existing users, etc.

It's not easy doing what WordPress did. Other major CMSs like Drupal and Joomla came and mostly went because maintaining the level of product quality and community is harder than it looks.