Well, I believe the exact opposite of this statement. I think it does exactly that: it helps give the slow games more XP so they can level faster. The fast games get less time XP but more actual XP. (Why do we have time XP in the first place?)
I don't understand what you are claiming here. How is my statement "If a slow game is 2 levels per year and a fast game is 5 levels per year, doubling RP will take the slow game to 3 levels per year and the fast game to 6 levels per year." not valid?
Maybe instead of posting a link to a different system, maybe you could post your actual proposal along with examples of how it would help the slow group without speeding up the fast group as well.
I also completely disagree. First, no amount of PMing will change how fast some people's lives work. If I have 15 mins a day, that's all I have. It doesn't matter who says what: time doesn't change. Second, I dislike encouraging confrontation between DM and player when it's possible to solve the issue with a rules change. Some people just aren't going to complain no matter how bad it gets - but they might just leave. Not everyone is up for confronting their DM and complaining about the speed of the game. So why force it? Better to solve the problem globally rather than depend on people complaining to fix it.
I wasn't proposing a confrontation between the players and the DM. I was proposing a discussion between them. I do think that nearly all players (DMs included) can be more due diligent in posting frequency. It's usually a matter of self motivation and desire. Most people have the ability to check and post more than once every three days on the boards, but not everyone does it even as often as once per day.
With regard to games with few encounters vs. games with many encounters, presumably players who think their adventure has too few encounters can again talk with the DM. If they cannot compromise, the player is always free to leave that game and move on to another one if the player wants a more action filled adventure.
I don't see how your rules change helps any of this, so please tell us how it does so. All your rules change appears to do is have everyone level faster.
What might help is for people to commit to a certain posting frequency and then live up to that commitment (shy of emergencies, vacations, etc.).