Just curious, does the gear purging code look at how much time you've played over X amount of days to determine when to purge?

I ask because I was out for a week, and then I've had two 30-45 minute logins over the past 3 or 4 days with no gear purge, then I logged in today and had a gear purge. Did I just fall below some average hourly threshold?

I also picked up a couple more limited items with my previous login. Does the bar you have to stay above climb if you get more limited gear?