How in the world can you know that the physics are better then Sonic Colors? Have you played Sonic Generations somewhere?
You can tell by watching the gameplay video-- the one with the interview that's spliced in. There's more resemblances to the classic physics than what you can see from Sonic Colors-- playing it or watching a video of it.
Also, Ruby Eclipse, a Sega manager (lol his opinion is null because he works for Sega) posted on Sega Retro noting an improvement from Sonic 4's physics. He confirmed that uncurling is not forced when Sonic is launched into the air (already an improvement) and that there are speed increases from rolling down a slope, not to mention the fact that you can break into a roll while running and pressing down.
Also, my theory, if it feels more accurate for you, I'll be happy to call it that, is plausible since this is developed by a different team of Sonic Team (the same team that developed Unleashed-- Colors was done by the team that has been making the "Storybook" games) and not by Dimps (Sonic 4)