Unfortunately it seems some of them have not yet realized that most people don't want to use that computer to surf the web, be it because it runs the crappiest OS of all times, because 2880*1800 is not a logical resolution choice or because it's just very expensive for no good reason.
Here's one example (most websites are like that) of a startup website that suffers from "The Retina Bias"
It's very empty, but then so are most websites on any big screen (from full HD on).
You can still see the phone, but the reflection is dead and so is the rest of the page content.
There are other standard resolutions in between, and all of them will result in a more or less useless combination of waste of space and lots of scrolling. Scrolling is bad. scrolling is ugly and annoying, scrolling hides what you're supposed to be showing to your visitors. IF you absolutely have to scroll, scroll one div, not the whole page. Be sure though that everytime you make someone scroll, a kitten dies.
What you should be doing instead
Basically what I do: avoid scrolling at all costs, try and use more of the page, think about standard resolutions and take the time to make a beautiful design (not like me).
On S3 > android > chrome
Sure, this website is ugly, but I'm not the guy who's supposed to have worked on his drawing skills, that's the designer's job.
Like it should be the designer's job to make webpage content usable for people without scrolls and without trouble.
In every example I used chrome without any toolbar, i.e. the thinnest chrome you can ever have and the best screen use possible aside from full-screen which noone uses.
The negative effects of bad webpage sizing are even more visible when you have toolbars, favorite bars, not-chrome or an Apple OS that thinks you shouldn't ever maximize your browser window unless you want to do that manually.
So please all of you MBP-retina-biased designers, design stuff that the world can use, not just people who bought an MBP retina and an iPhone7.
Fight vertical scrolling, kill page scrolling and please don't kill our bandwidth with retina size graphics.
If you want to think Retina, use svg, not huge static files.