Level 3 is a backbone provider, one of the largest by far. The CDN agreement with Netflix has no real relevance in this really. If Netflix had an agreement with another CDN like EdgeCast then Comcast would still be getting the same amount of data requested by THEIR customers. It may come from different sources, but it is still data that THEIR customers are requesting to have delivered to them.
Let’s assume for arguments sake and simplicity that Netflix CDN agreement is with EdgeCast and they have an agreement with L3 to be their provider of bandwidth (this may or may not be true). Who is Comcast going to try to extort to protect their video revenues now?
Are they going to go to:
Netflix and say our customers (Comcast eyeballs) are requesting too much data from you so you must pay us?
EdgeCast and say our customers (Comcast eyeballs) are requesting too much data from your customer (Netflix) so you must pay us?
L3 and say your customer (EdgeCast) has a customer (Netflix) that our customers (Comcast Eyeballs) are requesting too much data, you must pay us?
Now let’s replace Netflix with Hulu, Google, Microsoft, Vonage, Skype, or any other possible company out there that may have packets that Comcast customers want delivered to them. You see where this is going?
It really doesn't matter as in all cases the traffic is 100% being requested by Comcast customers. Level 3's request for more "ports" to connect to Comcast customers was to satisfy the eyeball customer’s request of Comcast, not Level 3's. If Comcast wants to limit the bandwidth being utilized by their customers because they are watching Netflix then maybe they should block Netflix or stop accepting ALL traffic from L3.
The reason they won’t do a single one of those things I mention above is because ALL of them (demanding money to deliver traffic or blocking/throttling traffic) are clearly a violation of the principles of net neutrality. They are trying to disguise this as a peering agreement. The only way this would be relevant would be if Comcast signed NetFlix as a CDN and L3 was demanding money from them.