Cheap blackberry Internet subscription. Why?

BlackBerry Internet subscription is no doubt the most affordable and price competitive data across all the major service providers in Nigeria when compared to other data plans both mobile and HSI (PC).
Let's take MTN for instance. MTN offers a 3 gb HSI night plan for 30 days at a cost of #2500. A 100 mb mobile plan for the same period of 30 days goes for #1000. While an unlimited blackberry subscription for the same period of 30 days goes for just #1500. It is still the same story for Glo, Airtel and Etisalat.
One begins to wonder why will BIS be so cheap and others so expensive?
In my opinion, I think it's the competition for the large Nigerian blackberry market that influenced this crash in prices of blackberry subscription. An advantage of a free market. To further get an edge in the blackberry market, some service providers allow tethering the blackberry subscription for use on non blackberry devices.
Though it is a welcome idea for those of us using BlackBerry phones. But it isn't fair to other Internet users on non blackberry devices who still need to cough out huge subscription fees. This obviously fails the 2nd of the rotary 4 wheel test; "is it fair to all concerned? "
What is good for the goose is good for the gander. There is still a large market of non blackberry users. Even Larger than the blackberry market. Who also desire competitive data plans at cheaper prices.
By so doing, many people will be able to subscribe to the Internet plans and stop try to figure out a way to hack into the networks and create free browsing 'cheats'.