No, absolute certainty is definitely not required. The cost is increased so a proportionate increase in probability*payoff is required.

Right, but now you've left the standard formulation of Pascal's Wager. The original Pascal's Wager includes the stipulation that one loses nothing by behaving as if God were real. To get to a point where you're willing to kill kids, obviously you have to go a lot further -- you must be ready to incur substantial costs as a consequence of belief.