It was somewhat inevitable that upon release the FIFA 13 Ultimate Team Web App was to crash with the millions of users based around the world attempting to log on at once.
The same ‘EA Sports Maintenance’ crash happened on the day of release of the FUT12 web app so it seems little improvements were made to cope with the high traffic this year around. Last time the web app was up relatively quickly and some people reported that it never crashed for them; so for the best chance of getting onto the web app periodically check the EA Sports Twitter feed for updates or refresh the webpage.