What does a user mean in this case - a single person or a family ? And how does this work in prime time, when 50%+ of the people are watching netflix etc, at 4 Mbps average(1080p + 720p), with other video services even less compressed ?
a single family (or a single connection to the network, anyway. One customer from the ISP perspective.)
You would think that at least 50% of people would be watching Netflix at the same time each night, but as of yet that doesn't seem to be the case. (At least not on any of the networks that I've been familiar with, which are in pretty tech-savvy areas like I mentioned, with heavy users.) It also helps that you can get one of Netflix's caching servers (can't remember what they're called) once you hit a certain threshold of traffic to their network.
The key though is that the more customers you aggregate the less traffic you can plan for per customer. So for example if you have 100 customers you might need to budget your network at 4-5mbps/customer to make it through peak times without slowing every one down too bad, while if you have 1000 customer you can get by with ~1.5 mbps per customer.
