This is correct. Diagnosing bandwidth issues between two points on the internet is extremely non-trivial. If you don't have access to every device between you and someone else, the best you can do is make educated guesses. Now, if he looked in the debugging info and saw:
"Throttling this luser's stream to 48Kbps, mwuahahahaha!"
THEN, that'd be something worth reporting ;)
On a side note, my data center's main bandwidth is provided by Limelight Networks. Some offsite backups are sent to a separate office building using Time Warner's commercial cable. Eight months ago, our throughput dropped from a steady 10Mbps to 30Kbps... for a month straight. Many hours of phone calls resulted in everyone finger pointing at everyone else. In the mean time, I setup a VPN between the two sites using IPSec, and was able to initiate a transfer through it at 10Mbps. The same transfer, outside the VPN, resulted in 30Kbps throughput. IPSec hides even the Transport layer data, so only source and destination IPs are visible (no TCP/UDP port numbers can been peeked at by prying eyes). Once they couldn't classify the service (SSH, HTTP, etc), whoever was throttling just let it pass.
Interestingly, once I harped on this enough to higher level managers, the problem disappeared :)
Don't trust anyone.
