Here's some stats. Some of it is actually somewhat interesting to read:
This has the average of several leagues at 76.8
Here it is mentioned that a goalie will have as high as 1/3 chance of making a save if he remains stationary.
Here's a lot of research into penalty shootouts.
I think the most interesting part is that in "sudden death" shots the success rate is only about 65%.
Based on my years of watching soccer, I would say that sounds about right for these kinds of extreme pressure penalty kicks. It's not as easy as it sounds.
Yes, to some extent it's more a game of nerves than a game of skill. But that's part of the attraction.