I'm not sure how they construct their sites (editor, templates, some kind of content management, etc) - but after a brief look at the code, the main element is set to left horizontal align instead of center.  It could be in the CSS as well.  It's been a while since i've done web development other than writing API's, so take that with a grain of salt

I used to have a client that used Moonfruit for their website so if you need a bit of help, just let me know