Even in DomII, events had requirements. I can't find any mention of it except for my own, and even then I didn't remember where I had read it from.
Sunray's site lists lots of (all?) events, and requirements for some. Examples:
A plague has struck the land. Empty cabins and rotting corpses litter the landscape. Half the population of the province has died. (Rare if Death 1 and common if Death 3).
Hordes of peasants have left their homes in search of a better place to live. (If unrest is 20+ it's a common event unless you have order 3).
This is from
http://www.freewebs.com/dominions2/events.html , and hasn't been updated for Dom3 as far as I know.