This will bite them in the ass. It has to be more expensive to produce and manage two sets of discs of the same movie. It seems it would take a lot of sales to absorb this extra cost. Also, I would actually PREFER the stripped version at the rental places once they go on sale. (and would be willing to wait until they were available for most of todays films) I hope it drives the price down though.
The only thing that would suck and I would not put it past Fox, would be to take the extra space on the rental to place an advertisement for the same movie disc and go on about all the "Bonus Features" you get if you buy the retail version. So they get a rental AND a sale.