Goalkeepers have changed a lot physically since the days of Schmeichel. Back then he and possibly Khan were the two leading/prominent keepers in Europe. Not exclusively but if they weren't the top two they certainly made up two thirds of the top three.
Big, burly, imposing, stocky feckers. These days, possibly due to the change in the balls, keepers are more naturally agile. Not that Schmeichel wasn't agile but looking at him it was probably something he had to work on more than the likes of De Gea does whose frame you'd assume was more naturally suited to leaping about the place. Keepers aren't as commanding as they were in terms of their control of the area during corners. It's as if some people think it's still 1995 when they gasp in horror if a keeper decides to punch the ball rather than catch it or stay on his line rather than charge down the angle.
De Gea relies on his agility and reflexes. Schmeichel - although he had both too - relied more on his presence and command. I don't think De Gea is near as good yet but I don't think you'll ever be able to make a fair comparison because they're different types of keeper.
), and he seems to have good friends within the Spanish squad so that might alleviate the pressure a bit.