- The best argument for what's weird is that undoubtedly good players who go inactive for a while can have an unusually low level. But if it's strictly the level, how important is that? Having a leaderboard based on level as opposed to estimated skill (another way in which the initial leaderboard might be a bit misleading, although this adjustment would not have produced a huge shakeup) seems to me to lead to some weird distortions in that way. Playing somebody who has fallen down the leaderboard because their random deviation is now 15 instead of 7 does not necessarily mean that your TrueSkill will be unduly punished.
The problem, as far as I can tell, is that it's not just the "level" that is affected by going inactive, it's the skill estimate as well. In other words, as someone posted above, you start out at a skill of 25 as of thirty days ago and then only what you have done since then counts toward your skill.
So, if a formerly-top player happened to only play one game in the past 30 days and lost, his skill would likely be somewhere around 23. This tells you nothing about his true overall level of play. Someone who plays against this "level 0" player will be unfairly punished for losing to this "lower-skill" player.