Resolution independence in OS X didn't happen because of UX issues - if given a very small space (16x16 or 32x32), a hand crafted pixel icon will generally look better than a scaled down vector icon.

For examples, compare the sidebar Finder icons with their full size counterparts, especially in the Places subsection. Some are scaled down versions of the larger icons (Documents, for example), whereas some are stylistic extractions (Downloads becomes a green download arrow in a circle).

I'd hope that when 2x mode comes to OS X for high resolution displays, when you take a screenshot in 1x mode it would use the 2x mode assets to create a higher resolution screencap, but that does sound like a lot of work for a very minor feature that would increase screenshot size.