I am wondering why in my dell studio xps 8100 does it have a 350watt psu

When my graphics card min wattage is 450? Thus my psu lacks 100watts according to nvidia's website. 

Source http://www.geforce.com/hardware/desktop-gpus/geforce-gts-240-oem-product/specifications

And also according to a computer engineering friend of mine... The i7-860 should be using a higher psu too.

So why is this pc built with such bs psu when obviously the parts require higher power! ?