The money has been followed
While I am a customer of Netflix and was convinced that Verizon was a group of digital gangsters as many as six years ago, one must be objective about public claims like this. Netflix has direct customers that are unhappy with their service, and they blame Verizon and provide understandable but not entirely provable graphics and metrics to point the finger. Verizon similarly has direct customers and needs to maintain its reputation, so it responds to such allegations with slightly less understandable and even less provable graphics and metrics backed up by a legion of attorneys ready to take Netflix to court. Both companies have customer bases to keep happy and both blame each other without a *real* way of us determining whose fault it might be (as much as I was already more than happy to blame Verizon, see "digital gangsters" above); looks like a Mexican stand-off.
Then, the white hat Level 3 rides in on the white horse and declares that Verizon is to blame! With no direct customer base to speak of, I would say they're far more believable than either of the two providers. Plus, you know, anybody else pointing a finger at Verizon is probably right in my book.