I used to have a blog on Wordpress.com and then moved to a static blog site. But I'm actually thinking of moving back to Wordpress because it gives you built-in commenting, stats, rss feeds, email subscriptions, tagging and search. Yes, you can include these features in a static blog but you'll likely be pulling them in from different services. I hate having to do that for a simple blog site. For example: commenting system from disqus (which I really dislike); email subscriptions/notifications from another provider such as mailchimp. Then possibly another plugin for social sharing. Then consider all the tracking data each service collects.
This might be convenient for you as a website owner, but this is not a good experience for the user (or a fast one). So there is something to be said for the all-in-one package that Wordpress provides.