Note how the person you quoted said 15" rMBP
Both sport the same resolution screen. Referencing the 13" rMBP as a comparison is actually a little more fair, since it has a higher DPI than the 15".
Edit: err...I take that back. The 15" Pro does have a higher res screen. I thought they were both 2880x1800. Though it still has a lower pixel density than the 13" at 220 DPI.
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You seem to be mixing up resolution and pixel density. But it's okay, Google does too.
Also, there's more to display quality than pixel density. It seems to be the new megapixel war in the mobile device world.
Either way you look at it, it's all just a numbers game. Very few people will be able to tell a huge amount of difference between the retina 2880x1800 vs. the Chromebook's 2560x1700 display.
Though honestly, DPI is a more important metric for determining clarity. 1280x800 might sound low res on paper, but it's crystal clear on a 5" display.
And no, display quality isn't just about resolution. You've also gotta take color gamut, viewing angle, nits, and other factors into account. Resolution is one part of a much larger whole.