Even if you're not the one actually extending it, the fact that it's easy to extend means there is a wealth of plugin offerings.
True. I hadn't done any PHP coding in many years, and knew essentially nothing about how WP worked, but Google + tenacity = useful results. Shortcodes, for example; super cool.
There are plenty of WTF moments in PHP and Wordpress but nothing that prevents pragmatic results.
Consider: http://wpmu.org/why-you-should-never-search-for-free-wordpre...
It has good documentation:
http://www.textpattern.net/wiki/index.php?title=Index
And an ecosystem of plugins:
The separation of editing and design roles in the admin is worthwhile as well.
// 1. Having built and hosted multiple WP sites scaling to millions of uniques a day, and even having built and managed a WP install for the most notorious domain name in the world, I have to say I don't advise it for most cases.
Once you drop the ecosystem there are plenty of alternative to creating static or near-static sites.
edit: I should point out that more alternatives for creating Web content is, on average, a Good Thing. Presenting a tool, however good, as an alternative to Wordpress however brings a lot of assumptions that may cause people to focus on the wrong things.
There's probably a market for a form of Wordpress that could use existing themes but not plugins, and only allowed basic posts and pages, with perhaps a more robust security model. E.g. prevent commenting (in order to avoid having to accept external content) except via Disqus or something.