HighRes Images for Retina display(Macintosh) is standard feature of Journal theme
It doesn't matter if it is a standard feature or not or LiteSpeed or Apache or whatever, but it is not a must have feature, so you could use it, but you don't must. Basically Retina display is not made for HighRes images. It increases screen resolution for better reading of text, so you don't need any functions to make your shop Retina ready.
There are two big problems you don't understand:
- Retina display can only be detected with Javascript. To detect it with Javascript page must be requested first and .js must be loaded from server to the client, but this process is too late. To get it work like you believe webserver needs Retina information with the first request, to tell the server: "Hey, I have a Retina display. Send me HighRes images and optimized CSS for my display." But no device with Retina display sends this infomation. That means, everything what you have done is useless and without any sense. You can use Retina support of Journal, but there is no need trying to detect for Retina.