I don't recommend doing ecommerce (directly) with it, or anything that could gather sensitive information, but for "just a website" with a bunch of cool stuff, WordPress is pretty much impossible to beat for the sheer amount of "cool stuff" you can do without ever writing code. The plugin ecosystem is tremendous.
The automated updates, so far, mostly stay ahead of the curve on exploits in the wild. We have a large pool of users to draw information from (thousands of servers running all manner of web apps), and we're far more likely to see exploits of systems that are harder to update; Drupal, Joomla, and especially a bunch of little apps that have tiny market share and small maintenance teams and cranky update processes. Having an easy and automated system for updates is just incredibly valuable for security.
What really needs to happen is everyone making web applications needs to start shipping a command line client for updates, that is safe/reliable enough to be run from cron. Best of both worlds: you don't need the app files to be write-able from the app itself (which is one of the big security concerns raised by this post) and you're always running the latest version even on systems that aren't being worked on daily. There's still the command line element to the problem, but it could be mostly automated away by control panels and installer tools (of which there are many).
There are a lot of forgotten CMS installations out there, and those are the biggest security problem, IMHO.