I it correct to say that downloading from PN Usenet costs PN much less than from othere sources. PN only needs to download the files onto the Usenet server once and after that it's distributed through its own network.
Yes, but cost for this sevrice are minimal compared to the cost of getting the data to the user.
To get data from the internet, into the PlusNet entwork is called transit peering. These are the connections to others ISPs and companies through which internet data travels to and from.
These links do cost yes, but for the volumes of data that can be transmitted, they cost pennies per user.
The problem is the cost of getting the data from PlusNet to the User. This uses links called BT Centrals, through which all data must travel, if it is to be supplied to a ADSL customer on a BT line.
Costs work out at about £1 per GB on these links. So for every GB you transfer, it is about £1. That makes it pretty easy to work out how much users should really be charged per month.
They are not because of the process of overcharging. Unfortunatly, the more people performing mor eheavy users, means more links need to be used to cater for all customers. This increases the per user cost significantly.