I could be wrong (this type of math is not in my wheelhouse) but I think your mistake is looking at them singularly in each event. They can't bust at the same point so they are never x% to win, it changes when one of them busts.

For simplicity's sake suppose we have a 10 player tournament and Ivey and Negreanu are obviously more likely to win than the other players:

Players 1-8: 9% to win
Ivey:14% to win
Negreanu: 14% to win

you're looking at it as if they have a 28% chance to win, which they do at the outset. But with 5 players left suppose Ivey is eliminated, Negreanu is no longer 14% to win, his equity jumps up to about 19%, so even when one is eliminated the other gains, and in 100-150 player fields the added win-equity could be pretty substantial, maybe as high as 1-2% depending on when the other player busts, and even higher at a final table. Over the course of 50 events these .5%'s add up.

You have to calculate it as if they are 28% to win at the start only, but when one is eliminated you have to factor in the other's new equity which will always be + (how much depends on entries, current chip-stacks and how far along the event is). The way you calculated your odds doesn't account for this readjustment when one of them busts and the other is still in it.