Every day the regional rules for a data center are reset. One of the new rules that the NPC's who play by regional rules (not all do) have might be Roulette. It's totally random if one, many, or any of the regions will happen to have that rule on any given day. I've been using (and updating for Aether when I can) the site Kalandros linked to for a week or so now, and it is accurate. I see at least one region on Aether with Roulette maybe every couple days, and some of the days have had like, four regions with Roulette. It's just pure RNG who gets what each day.