I think you're missing the point. This isn't about penalising having a separate mobile and desktop site, or even automatically redirecting phone users to the mobile site. It's about penalising sites that automatically redirect all mobile visitors to the mobile version's homepage, even if they tried to visit a specific sub-page (eg an article on a news site, product on an e-commerce site etc) through Google search. Which already falls foul of Google's existing rules against serving completely different content to Googlebot and real visitors.