It reads to me like you won't have the choice of keeping the grandfathered $30 unlimited plan if you upgrade your device as has been the case before.
IOW, I can keep my unlimited as long as I stay on iphone4s, but the next iphone iteration won't allow that.
So, you're gonna want the $30/3GB plan, whether you want it or not.
Oh, and they aren't stupid. They meticulously analyze customer usage patterns and then determine the best way to hose us down in the bent over position.
I imagine they don't want that kinda bad pr. The current LTE phones are still unlimited with the grandfathered data plans...