
In Belgium the situation is a bit special: Belgacom owns the ADSL lines to your house (the last mile if you want) because it was the national operator. However this arm of belgacom has to "rent" the line to other ISPs to allow you to take an ADSL connection. You are then billed by your ISP for the ADSL connection and traffic.
Belgacom also has it's own ISP service, previously known as Skynet.
In my case I am an EDPnet customer for my ADSL (because they offer a much better deal than belgacom skynet) and THEY set the download limits for my account (up to 60 Gbs). Of the money I pay EDPnet, a part goes back to the arm of belgacom that owns the "last mile" for the rental of the ADSL line from the exchange to my house, but belgacom has nothing to do with my traffic, just the rental of the last mile line to EDPnet.
I am not a belgacom customer! Counting me in the 90% because my ISP has to rent the last mile line to belgacom is not correct. If you count only the customers that have belgacom/skynet as their ISP the number would be much lower.
The only reason I can see to get belgacom as your ISP is if your employer actually has a contract with them and offer you a discount.