I don't care one bit and I don't really understand why anyone else would either unless they're just staunchly anti-region locking for everything in every case. I guess if that's your opinion on things then you have reason to be upset.
I'm guessing it was either a requirement by the TV programming partners for netflix/hulu/amazon etc, or simply a QA issue, not able to guarantee that every aspect of the system works perfectly with firmware regions mixed between console and gamepad. Both pretty reasonable reasons to lock the gamepad with the hardware.
I could see why the content providers would see the gamepad as more than a controller since it is used to display content and requiring that the hardware (meaning the gamepad also) be region locked to meet obligations to CBS, NBC, Sony, Universal, etc and avoid legal trouble.
Also it's an easier solution than cross-QA testing every region's firmware (since the GamePad does recieve firwmare and updates) as a mix between console and gamepad. Make sure the system works perfectly with a US system, japanese gamepad, European System and South American Gamepad, etc.
I just noticed a lot of people are getting upset on NeoGAF over this and that forum is notoriously over-reactive over anything restrictive about hardware and have a lot of very vocal Wii U detractors.
Being that the gamepads are not for sale individually and no games support more than one I see no reason why anyone would care about this - I think you'd have go go out of your way to be affected.