Actually these days all masts are technically constant curve bends, but there are variations on the theme spanning from the flex top to hard top ranges, with the middle range being those most compatible the biggest segment of sail brands. The bend character of the middle range is arguably best represented by the 64/76 curve, and they tend to be manufactured by mast manufacturers that aren't involved in sail design and manufacture. There's some tolerance to these numbers, but the greater the variance leads you to either the flex top or hard top ranges.
So when considering sails to buy, it's the buyer's responsibility to learn more about the recommended bend curve for the different brands. The Peterman listing offers an outstanding resource for judging the bend character of different masts, and it also reveals what's ideal for certain sail brands, especially since many sail brands are having their own masts built to their recommended specifications. So, even though different mast brands can be manufactured by the same company, the character of the brand masts can vary a lot.