In the long-term, as @Ashley said, why would you purposely slow your game down for machines that can handle it better? Though I say that with not really being worried about mobile right now, nor having tried C2 projects on mobile, so take this with a grain of salt, but...that seems kind of silly and short-sighted, and indicates to me it may be high time to see about optimizing your project if you're having framerate issues. The technology behind how C2 works is still relatively new, and it's only going to get better...so why hamstring yourself when there's so many interesting developments going on in the HTML5/javascript/jquery not to mention C2 world?
@jayderyu: That's a 100% false equivalence. Gears of War was designed to run on ONE specific machine with a known featureset and hardware configuration that is/was incapable of running the game at 60fps. C2 games are, in general, not developed under such rigid requirements. Comparing the two is about as inaccurate a comparison as I could imagine, putting aside the huge technological differences between the engine running GoW & C2.
60fps has for decades been the goal of game developers (on computers, at least, and in general consoles aren't so different) as that's just about where humans aren't able to tell the difference in fps any more. There's no reason that goal should change just because some hardware isn't capable of achieving it, and as it's been settled on as the standard refresh rate for LED monitors - I think worldwide? Not totally sure, but pretty sure - for some time now. The argument that prettiness outweighs gameplay & smoothness/responsiveness seems counterintuitive.