Do you really think "almost all" designers use a specific model of a specific computer that shipped about six months ago? Hell, I consider myself a half-assed designer and won't upgrade to a retina MBP because a) the screens have issues b) the web has issues and c) most of the design software I use has issues.

Designing websites in a way that only works well on retina displays has to be one of the most ridiculous examples of the Silicon Valley bubble in recent memory.