Entirely valid point, but there are ways to handle that as well (tor networks come to mind), but it does devolve into an arm's race. Where each side is spending more time/energy protecting or cracking a packet to charge it at a specific rate.
That's not a viable solution. Unless the TorProject has made MASSIVE gains since last I checked, it's simply not viable for low-latency or high-bandwidth use. It's not like everyone on Comcast could feasibly switch to getting their Netflix through Tor.