hmm.
Thats an assumption 10mbit is full of light users.
3 people in my family alone are on 10mbit and use way more then I do, on 30mbit I am using under 30 gig month, and they using over 100 gig easily on 10mbit with torrents. One of them also has kids so they will be using bandwidth as well.
10mbit is quite capable and is still double the speed of the average adsl connection, even using it half the time will push 1.5tb.