"...even in the absence of robust broadband competition, network owners are likely to find deviations from the end-to-end principle unprofitable."
As a counter example to this, a very popular cable company where I live offers VoIP phone services, and lowers the packet priority of competing VoIP vendors.
My point is that network owners can clearly deviate from the end-to-end principle for profit, and my example of this is a cable company which restricts the bandwidth for services in competition with its own.
If you would prefer, we can treat the situation as entirely hypothetical. Do you disagree that a cable company with a large market share offering VoIP services could profit from restricting bandwidth for other VoIP services?
First, there's a signalling problem. Users buy Vonage, it's terrible. Why should they believe anything the incumbent ISP says about VOIP, unless the ISP fesses up to meddling with their traffic?
Secondly, how will they identify VOIP traffic ? If such practices become pervasive, folks just won't use plaintext SIP/RTP anymore.
Your first point seems entirely unrelated to the hypothetical situation.
With regards to identifying the traffic, that may be a valid concern and I cannot claim the knowledge to argue with you about it.
However, assuming the ISP were to discover some practical way to identify the traffic, it stands to reason that they could profit from reducing their bandwidth.
As a counter example to this, a very popular cable company where I live offers VoIP phone services, and lowers the packet priority of competing VoIP vendors.