Why does Delta Rostock Mini require so much Torque?

I've been considering to build a Delta Rostock Mini. But the guy said that it requires nema 17's with 4.3kg-cm torque?! Why in the world would something so light require so much power? Is it friction in the joints of the end effector? Or is it that he wants crazy speed? I don't get it. I'd like to double check this before I start building something with smaller motors.

I think at least the extruder needs that.

To add to that, nema17's are way easy to get, you can get a 1.68 or 1.7 amp version, they have 2000grams/cm torque if I remember it well.

Why don't you ask 'the guy' or ask it in the topic where this model is discussed?

Heres the wiki:
[reprap.org]

And I quote:

Quote
Note: This image shows NEMA14 stepper motors rather than 17 but they don't work - not enough torque. Will update once 17s are installed.