Wow, nice effort there op. Well to answer your question.... uhhhh yeah I'll just start saying stuff without any type of transition.
End game content is probably the biggest concern of the dev's at the moment, (Feel free to look for Bashioks posts on the subject) and one of the oldest mentioned are the "Endless Dungeon" where monsters become progressively stronger/difficult and then the pvp aspect of the game (which correct me if I'm wrong, but I haven't heard anything really).
Having monsters change from their static stats along all games means the game just has that extra level of complexity many may not want. Just throwing this out there, but if monsters throughout the game are constantly becoming stronger to keep pace with you, why even bother to get better gear? The game itself should become progressively more challenging, yes; but the act 1 monsters should remain as easy/difficult as they were the first time you saw them. (Of course this disincludes when more players enter the game and monsters amongst all ranks become stronger).
You're on the right path and I agree the game should remain difficult at some level, just not all of it. Monster scaling is not really a good solution.