I don't know if there was ever hope for resolution independence in Lion, but this pretty much quashes it. For a Summer release they'd need to give developers more notice (unless there's some magic way they're offloading all of that responsibility to the OS).
It's a polarizing debate raging on these forums that will never resolve, but I'm in the camp that really sees a benefit to "retina" (not 300 dpi) density in a notebook (or iPad). Looking at web pages on my iPhone, I know how text and icons *could* look, and it's really pleasing. As if it's a glimpse into the future promise of notebooks that only exists in our imaginations ...
Websites are still built for low dpi screens. You will get sharper text and general layout but any images/icons/decorations will look like thumbnails.
Res independence on the web needs full CSS3, SVG, and faster broadband to work.