Network latency and network bandwidth are 2 very different thing that can have profound affect on game play. Its really hard to track these type of problems down because everyones got a different network. Many people have nated networks and have multiple computers.
What makes this worst is the stupid auto update on many computers. Firefox does this in the background so you don't know whats going on. Others have macbooks which also does autoupdates. Me personally, I have a mail server I shutdown temporarily during games.
Many company have taken the business decision to just download the updates first then ask you if you want to install. This also has an affect on people with small pipes.
At the end of the day this game is very latency sensisitve and I don't believe the packets are very large (so bandwidht useage is small.) Last time I checked it sends out and receives roughly 30-40KB/s on an average 3v3 map. This is easily doable on most peoples network but are on the edge for DSL users in the west coast since ATT sucks.