From a summer release, Segs's moved Sonic 4 out and delayed it again, to nearly the end of the year. here was never any official release date, but if there were you can still expect to tack on another few months of waiting.
According to Sega the delay was to receive feedback from its fans and try to use their suggestions. This was written on their blog:
"For the first time ever, we've mixed internal suggestions alongside fan feedback to make some new, positive changes to the game. Yes, you just read that correctly. You're not dreaming."
I'm not sure what you mean, though. Sonic was built to run fast. It only makes sense that his games should be released fast.