What you are referring to is when several ISPs had congested peer links with L3. L3 Peering where Netflix had chosen L3 to be a CDN into those ISPs had degraded service. This was not unique to Netflix or Verizon. The L3 settlement-free links were congested by unbalanced CDN traffic, and as it pertained to going into those ISPs, this affected all transit and CDN traffic from L3.
For other CDNs like Akamai, when a peer link gets busy they just requisition more peering. They did not suffer any of these problems.
It appears that the dip coincided with Netflix's rollout of Super HD quality to its entire customer base.
http://blog.netflix.com/2013/09/highest-quality-hd-now-available-to-all.html
http://knowmore.washingtonpost.com/wp-content/uploads/2014/04/isp-speed.png
I understand.
It is illustrative of the suspicion, founded or not, that they have an incentive to break things.
One of the cable companies was blocking Skype for a while because it competed with their telephone service and now some of the wireless providers are breaking TLS transactions on their email servers.