It would be hard to prove someone shared info via PM though. It's easier with an SD case, because, it's possible to see it through the log (For players). Plus, i think this would give BoB users a BIGGER advantage then they already have, because they can tell what they lost easily, if you're a user who plays from an iPod/mobile device or a browser without the Add-on, it becomes exponentially harder because you may not exactly remember where all your territories were. At least with Bob you can tell exactly which territories you lost.
And Herbas has a point, once you get big enough, you are almost unstoppable unless someone called you out in the chat. I've played with enough quiet people to know it happens. At least with the game log you can tell if someone is getting big. Without it, well, you depend on the other players as much as yourself.