@merrit - Because it has not been a focus of laptop manufacturers. Instead the focus has been faster CPU's or bigger hard drives. Going premium on the display, means you have to cut on something else to deliver the laptop at the same, and I don't think Intel is going to cut on their CPU prices anytime soon. In some laptops, Intel's chips take up to 40% of the BOM price. That leaves little wiggle room for experimenting with high quality displays.
The good news is that the popularity of high resolution tablets will also force laptop makers into a trend with higher resolutions, too. Asus for example is one of the leaders of this trend, and has even 11.6" laptops with 1920x1080 resolution.
My eyesight isn't great, but I can't tell the difference between the resolution on my "retina" devices and resolution on other screens. Can most people tell the difference?
If not, this marketing and competition on resolution may be distracting us from issues that have a bigger impact on our usage experience.
I'm 20/40, and it strike me as amazing up close. Desktop distance -- not so much. I have a 27" iMac, and I can barely tell there are pixels. But since iPhone 4, it's been Retina all the way. The Retina 4G iPad arguably changed my life. All of a sudden I can have a full page of a pdf in bed, triple-clicked to negative color, and the text is still perfect. Naturally as soon as the Retina macbook came out, I was in heaven: I can line up two full-width documents, read one and type another (usually one is in LibreOffice, the other is in Papers or Chrome, but emacs is behind LibreOffice).
So with a briefcase full of Retina, I'm quite happy. But the 27" iMac still feels like the most spacious screen. The other thing the Apple hardware has going for it is that I can tether my MacBook to my iPad's 4G network via bluetooth, so the iPad doesn't even have to come out of the briefcase to be incredibly useful, and saves me having to have another data plan. I note the Nexus 10 does not come in a 4G model. That seems crazy to me.
I have slightly worse than 20/20 vision and I see a huge difference. The retina iPad that I had was amazingly clear compared to my 1600x900 17" laptop screen and my 1200x800 tablet. I recently looked at both the retina macbook and an asus 13" ultrabook in best buy last week. The macbook retina's screen was noticably sharper than the asus' 1080p screen, but 1080p on a screen that size still looks absolutely amazing. I would honestly be happy with either one.
The good news is that the popularity of high resolution tablets will also force laptop makers into a trend with higher resolutions, too. Asus for example is one of the leaders of this trend, and has even 11.6" laptops with 1920x1080 resolution.