The majority, if not all, sanctioned WFTDA bouts are now three TWO periods. It's been literally years since I reffed a three-period bout.
It also makes no sense for a balanced switch off of jam refs to have three periods.
[EDIT: Drrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr]
~j.z.
Clarification:
ALL sanctioned WFTDA bouts MUST BE two 30s. While the rules allow for three 20s, the WFTDA sanctioning bylaws do not. I think that's been the case since June 2008, but a WFTDA rep would know better.
Three 20s remains in the rules because in theory a WFTDA league could use it for intraleague bouting. Also maybe because it keeps the ejection totals in there for abbreviated two 20s bouts you might do for double headers or B team openers. And for the newer non-WFTDA leagues that use the rules.
Three 20s went out with high button shoes. Both options were in the rules since I think 2.1.1, but few leagues used two 30s unless it was for doubleheaders. When they set up 2007 Nationals, the participating leagues voted to go with the two 30s format, presumably to save time. Those that got accustomed to this format found that they could make it through a 30 minute period while those who were new to it could start to falter toward the end of the period. Add to it that they could still manage a three 20s bout with no problems and the writing was on the wall. Once 2008 hit, almost all leagues immediately switched to a two 30s format.
The weird thing about this one is that because so many leagues had opted to switch to two 30s right after Nationals, sometimes folks (like me) weren't aware that this had been officially made WFTDA sanctioning policy. Some league's reps probably didn't bother mentioning it to their skaters and refs since they'd already made the switch to remain competitive.