Just one opposing data point -- I frequently switch between a 13" MBP running at 1920×1200 and a 13" MBA running at 1440×900 and I can't really feel a difference, let alone feel it's a nightmare. I wouldn't enjoy squeezing back my IDE to the MBA screen, but that's about it.

This is true, but the parent specified the retina MBP, and that does make a difference (in my experience, and others I know who’ve tried). Retina displays will spoil you quickly. I live with HD/HD-ish laptops for battery longevity, but even the retina tablet display can be jarring.