Nintendo loves to produce peripherals, because there is a lot of money to be had in peripherals. That is about as far as the strategy goes. Your looking too deeply at something that isn't there. On the point of denying technology to others all Nintendo peripherals are based on existing concepts or technology. Nintendo isn't so much inventing them as applying them. That said if they can do it then so can the other guy.
I honestly think it is a poor strategy in the long term. While in the short term it makes Nintendo money. The problem is that eventually it antagonizes consumers and third parties. Which usually results in a loss of faith. How easily we forget the disasters like the 64DD, Super Scope, Power Pad, Four Score, and the ram upgrade module. When you shovel out peripherals your going to burn a lot of people when it becomes apparent that they were unnecessary.