I guess after a while Mobil decided to end confusion about "High mileage" name, because some of the new cars were and still require 10w-30. On mobil's website you can find a whole bunch of questions and aswers about 10w-30 and "high mileage" name. There is nothing special about this oil no matter how you call it. I suppose they wanted to call it high mileage for some reason. They didn't change formulation just put a new label.
Actually, this is kind of funny. Mobil claims that engine with their oil after 200k miles showed "virtually no wear." If person had been using 5w-30 and mobil recommends using 10w-30 after 75k miles that means that mobil 5w-30 does cause wear if you need heavier oil.