I guess we just define "probability" differently. My way of thinking of it is that probability is a measure of chance.

Think of it this way, a flipped coin in the air has a 50% probability (chance) of landing heads up. However, once it has landed all probability (chance) is removed; it either is heads up or it is not heads up.

So it is with hets. They either are or are not. I think people use the 100% to indicate it is indeed an actual het while the 50% and 66% ones are still "coins up in the air yet to land" as it were.

Because it is SO common to see 100% used in advertising hets, it has to be considered, and needs to be clarified
I agree it is good to clear things up