The upcoming DmC runs at 30 frames per second on console, but Capcom claims they've stumbled upon some techniques while using Unreal Engine which give the feel of 60 frames per second.
“60 frames per second is a speed the brain and the eye can catch up with and understand,” says director Hideaki Itsuno. “But at 30 frames per second there's a technique where you take advantage of the brain's ability to fill in the blanks.
“So even though you have it running at 30 frames per second, you create the motions and the poses in such a way that the brain will naturally fill in what would have been the extra frames.
“Also, on the players' side, we made some adjustments to the button response and when it's reflected on screen.”
As for why they chose 30 over 60 in the first place, this was for artistic reasons -- going to 60 would mean "very static environments and less combat effects", when they wanted to go big and "[have] the city feel like it can manipulate and move".
PC players don't have to worry, though: you'll be able to run at 60 (or possibly higher) and get the rich environments.