Sure, he holds the ball and that helps some guys get open, but he still has to be accurate. There also plenty of times where he has to fit the ball into a tight window... look at his last throw of Super Bowl XLIII.
Ben has definitely never been one to shy away from throwing into tight spots or into coverage, and he usually winds up with pretty good results.
Even if he did get all his completions from wide open passes and wasn't extremely accurate, it wouldn't explain why his accuracy ratings are almost identical to Mark Sanchez... Big Ben is every bit as accurate as any of the top 10 QBs in the league and the ratings should show that.