It started when I played a very highly regarded player here and was able to beat him. He was complaining about lag and it seemed pretty much lag free to me.
So, he developed a test. We would both use Kenjutsu and punish one another with attacks that should have equaled zero - making both players safe on exchanges. So, he would attack me. I would block it and immediately come back with the same attack - which theoretically he should be able to block and come back with the same attack - so that we can go on infinitely blocking each other's counter-attacks...
Only, I could block his counter - but he couldn't block mine. Since we were just holding block as soon as the attack ended - there was no room for user error. The test worked and proved that the lag was NOT the same for both players. Since then, players from here have used this test - and developed others - and they all yielded the same conclusion...
...that lag is not always the same for both sides.
It does offer a nice pre-game test for assessing the fairness of matchups online, but the results yielded are completely undeniable.