Maybe people who use too much data are being shunted to the 4s specific plan... I upgraded my wife's line (she only has the 200mb plan) and will swap phones with her, so I didn't see any effect this go around...
That makes no sense. I think the people who use too much data would be promoted to use the higher data plan, such as the $45 one, or higher. Them dropping "unlimited data plan for iPhone" and applying "unlimited data plan for iPhone 4s" is not a big deal. Chances are, when the next iPhone comes out, the same thing will happen. You will have to drop "unlimited data plan for iPhone 4s" and add "unlimited data plan for iPhone 5."
People are making this a much bigger deal than it is.