Looking at the code behind Wordpress there are several classes that it uses to accomplish certain things. For example, Wordpress uses the IXR class from Incutio as a XML-RPC server/client. Doing this saves the Wordpress developers from re-writing things that other people have written so that they can concentrate on the important things.
The most impressive thing about Wordpress is that it is completely free, which I still have trouble believing. If you are running a blog then you should consider moving over to Wordpress or at least give it a go if you haven't already. You can get it from the Wordpress website and use the famous 5-minute install to get going.