It used to be separate from audioscrobbler.com (the charting and recommendations service) and only did streaming 'radio' based on your AudioScrobbler account.

It used to be separate from audioscrobbler.com (the charting and recommendations service) and only did streaming 'radio' based on your AudioScrobbler account. I'm guessing that, they realised that while AudioScrobbler is an okay name, Last.fm is a better one (it's short, easy to remember and implies something to do with music/radio) and merged the websites.