I noticed this the other day when updating my page. I still upload in low res, as the low and hi res versions looked exactly the same to me when I did a side by side comparison.
you can see the link on my page
http://www.facebook.com …338.21318.125301070816209
they should all look the same on facebook... facebook will still compress your high res image for their site.
however, i did just download your image in high res. all 18x28 inches of it.

