Re: I've always wondered...
All the technical discussion of fields in IP datagrams is irrelevant.
What the content providers in the US are determined to get - and bribing, sorry, lobbying polititians for - is the right to pay ISPs to ensure that their traffic - based, I presume, on source IP address or by deep packet inspection - is prioritised over everybody else's who hasn't paid the ISP, regardless of purely functional requirements or indeed the value of any QoS fields in their or others' datagrams.
If every piece of routing kit on the whole Internet honoured QoS fields - although exactly how to interpret them would have to be agreed internationally and by all equipment manufacturers first - all that would happen is that people/companies would abuse them to ensure their web site loads quicker and so on.
Given that reality, the best option for everyone other than the big content providers and ISPs is to press for a situation where by and large all datagrams are treated equally, except in the case of emergency services and to quash DoS attacks.
As I and others have pointed out, streamng video works absolutely fine this way if the recipient ISP provides a decent sized pipe to the end user because it can be buffered. It would be nice if VoIP/video-calling/conferencing was seamlessly high quality and low latency but it's not the end of the world if it drops out now and then. ("Sorry, didn't catch that. Can you repeat?") but in any case the protocols developed for this are now very good at coping with a jittery channel by rapid, dynamic resolution modification.