TEDx: An effective Teacher must be less helpful

I have found this TEDx video on May 18th, and blooged about it on my Anas’ Thining Zone blog. I thought to migrate it to this one for I will need it for my PhD research.
Watch Dan Meyer video (11 min). He is advocating teaching Math in a new way where students define the problem. One interesting outcome he suggests is that teachers should be “less helpful”… How can being less helpful more effective in teaching!? Could this concept be applied in subjects other than Math? What are your thoughts?