Do you think Rolex should offer both types of steel depending on user needs?

[ph0t0gen1c]

I was pondering who actually benefits from Rolex's use of 904L steel over the standard 316L?

Surely using 904L pushes the raw materials costs, machining costs due to special tooling, and yet the majority of users probably take their watches deeper than a swimming pool. Am I missing something here, would it not benefit Rolex having 2 versions of the steel in a particular model to offer those that don't need it a choice, and is it not over engineering for the sake of it?