I dunno why they wouldn't display both. Also cynical me thinks this is a more useful change for advertisers than users.
That said this would probably be useful for post ranking on the back end, if they're not already using it. There's always been a noticeable thing on reddit where posts on large subs with little activity don't seem to bubble up much on /r/popular. Which makes those subs seem even deader because they don't get new blood.
Well it shouldn't be a surprise to anyone, but Randy Pitchford is really good at providing ammo for these types of headlines. Guy needs to learn to keep his mouth shut sometimes.