It's not just that.
24fps film has a shutter speed of 48/1, meaning if you film at 48fps with 48/1 shutter speed, you can extract a 'perfect' 24fps version of your 48fps film. If you move to any speed faster than that, you can't produce a correct 24fps print.
well, Trumbull has shown that you can very easily get a normal looking 24 fps when you shoot at 120 fps, by blending three frames and skipping the next two. there's some examples on youtube that show his blended frames vs a normal 24 fps shot and it's pretty impossible to tell the difference.
so, if you want to project at 60 fps, shoot at 120, and you've got all bases covered.
i hope that we aren't just getting twice as many frames with a 48/1 shutter speed in the hobbit though, because a big part of the push for going to higher frame rates is about reducing motion blur for the sake of 3D projection. the blurrier each frame is, the harder it is for your brain to resolved fast motion into a 3D image.
lack of motion blur is part of what makes stop motion animation looks so incredible in 3D, and part of why video games really pop in 3D too.
i hope they're shooting the hobbit at higher shutter speeds.