Staff do seem to be saying that in a few posts.
But if they really are counting the traffic per customer there is no reason not to tell the customer. I have grave reservations about their traffic accounting.
Not a big issue to me either but Plusnet do have customers on limited accounts who need to know what is being used and also if this youtube/netflix traffic counts against their allowance too.
It is just another woolly not thought through issue. Plusnet still have not answered the question about the effects of this change on the legacy accounts.