Nope. Rogers tracks everything through your modem. They *may* be subtracting an allowance for things you can't help.
Yes they do substract an allowance for internal traffic...That they have no choice about..... Usually things like ARP packets and any number of other bits and bytes that could possibly get added into your monthly total.... All providers do this as standard practice....If they didn't you could easily loose 20 GIGs or more a month of your cap depending on the type of network......
And as a quick side note Cellular providers to them same thing with certain types of traffic with PDA and non PDA based devices.....(and yes rogers is included in that) -- common sense isn't so common....is it?