[paledot]

I don't think this is a coincidence. Salt water, after all, is present in effectively unlimited quantities in many of the world's major cities. If the price of desalination drops, competition (in an imaginary world) will drive down the price of desalinated water in lockstep with it.

Interestingly, there is a theoretical floor to the amount of energy invested per unit of water desalinated, and we're apparently quite close to it. From here, our best hopes for improvement are to use waste heat or solar thermal energy to desalinate water.