Looking at your site, decay is working correctly.
Look, for example, at Tehcheat on your site:
http://rfte.dkpsystem.com/memberprofile.php?memberid=5#dkpYou'll see, if you scroll down his attendance list that the "Worth" and "Earned" columns for older events are not the same for him. The "Worth" column represents how much it was originally worth, and "Earned" represents it's current value.
So, as an example from his page, Look at the "On Time Bonuses" for 7/27 and 7/28.
You'll see both were originally worth 25 points, while the 28th is currently worth 23.5 points, and the 27th (being older than the other) is currently worth 23 points.
This discrepancy is decay working.