To provide Turbine with data. I am a professional software developer, and while I have no expertise in network communications, the one thing I know for sure is that debugging is a LOT easier when you have detailed information about the problem. And I consider it "obvious" that they haven't isolated the problem yet, or they would have fixed it. (The alternatives to this assertion are too horrible to contemplate)
Client-side lag is totally different and easily identifiable, since it only effects you. Obviously they cannot fix that.