Didn't notice any bugs, but haven't tested for bugs. Used it and it works great - favicon.ico is much small than that other thing I used in http://nashape.com/blog/2012/09/12/big-favicons/. Great work! (especially because you did it in PHP which, after 10 years, I don't think I can face again...)
Sorry about that – the point of the article definitely wasn't to exclude non-Retina users, it was just to document what I was encountering when I came to creating a favicon for the site.
You don't think screen resolutions will continue to increase? I give it a couple of years, maybe less, before the "retina" resolution is standard hardware.
That's most likely going to be a >200dpi screen, where you can simply use 2x upscaling for better performance (with no visual degradation compared to current monitors).