This is interesting. I'd caution basing anything purely off number of accounts. In 2011, I would bet that the percentage of multiaccounts was quite a bit higher than it is now. So while we likely do have fewer players, it is probably not quite as different as those numbers would indicated.
The Purge likely lost some players, but personally, probably no more than we were already losing because of obnoxious behavior, so I'd call that a wash.
We did lose a number of great players, who had a strong presents on the site, which I think has given new players less to aspire to. More importantly, though, I do truly believe that while the game experience has improved for veteran players, it has likely become worse for new players. When I first joined, I almost immediately started playing with some of the best players on the site. There were no rankings, no records of NMRing, so no one cared about playing with new players. I can imagine it quite hard for a new player to become established here now. And, let's face it, if your first game isn't fun, you probably aren't going to stick around.
Finally, we've lost most of the tournament and series games. Those who weren't around probably can't imagine, but we constantly had at least 1 if not 2 tournaments running that were well populated. We also had a variety of series games. All of this adds to the community and helps keep around.
Anyway, those are just my thoughts. Although given the dates involved, I'm probably a bit biased <3 <3 <3