Well, I've heard operators think that getting rid of the top tier customers is a good thing, since that means that the other customers would have more bandwidth to play with, and the can postpone investments in network upgrades (and node splits)

Well, since the report is provided by Arbor, whom bought the DPI vendor Ellacoya some time ago, we can probably pretty safely say that changing the port doesn't matter.

That's a good point. The negative side of it is that most of the P2P apps always sets the highest prio, so it doesn't work very well anyway.

Look at the traffic with DPI is unfortunately the only way to be sure of what apps has which DSCP flag, and even enables you to rewrite this flag to match what you really think the particular app should have in your (as in the ISP's) part of the network.