This is just silly. Are there legions of websites that work on non-Retina computers that actually break on the Retina MacBook Pro (rather than just looking bad)?

Web designers should not default to the latest-and-greatest. When they do, they often produce sites that are completely unusable without it. Web designers should spend more time worrying about users that don't have the latest-and-greatest (aka most users).

Most web designers need old laptops and low-end smartphones far, far more than they need a Retina MacBook Pro.