The default triggerStatements seem to have changed since the Jets DLC update (1.70)
I believe they used to be: ["this","",""] in the form of [cond, activ, desactiv]
since 1.70 they are now: ["true","",""]
This means that existing missions and modifications that create scripted triggers that don't explicitly issue a setTriggerStatements command are broken. As is the case with the Zombies & Demons modification, for instance.
If one were to create a scripted trigger, set activation to "WEST" and "PRESENT" using setTriggerActivation, but not issue setTriggerStatements (because perhaps the trigger is only used for a triggerActivated check), the trigger would automatically activate regardless of the presence of BLUFOR units.