Of course, anyone can use any lens wide open. It's when you really look at detail (the more you blow it up, the more it becomes noticeable) on the edge of the frame, you'll see more distortions. I'm not quite sure how the actual glass lenses are manufactured but the edges are harder to manufacture accurately than middle part.
I haven't been following the latest manufacturing processes but I imagine with computers and laser cutters, today's lenses are much better than they used to be.
