Does it really though? The netflix stats show that at most it's a 2x saving: http://3.bp.blogspot.com/-72J2TkcP4j0/TxcdvDk58VI/AAAAAAAABA...
And EC2 is more than 2x as expensive as dedicated...
Don't get me wrong, EC2 has advantages, but it's not cost (unless Netflix is paying much less than the public prices, which is possible).
That's only for NA
Yes, Elasticity is THE advantage for Netflix when it comes to using EC2. Consider the vast differences in usage they have in North America during the evening after dinner vs during the middle of the night. I can only imagine their fleet capacity goes up and down drastically every single day. This amounts to huge savings over having the bare metal.