Thanks all for your reply. We are looking for prestigious medical programs with short duration. Oxford fits perfectly on paper. But seems its admission process is not very friendly to international students and there are quite a few hurdles for US students to cross if they want to practice medicine in US after graduation. As all suggested, applying Oxford medicine does not seem to be a viable path. Probably many people realized this so they did not bother to apply.
Being the parent of an elite US boarding school, I have seen so many talented kids. The academic vigor we have is nothing less than UK standard. Sadly, it is really their loss.