From the article.
Leica makes a lens the way it should be made, with metal and glass, while everyone else is making plastic lenses that are meant to be thrown away in a couple of years,” said Ken Rockwell, a photographer and expert on cameras and lenses. “The Leica lenses are so special because they are smaller, faster and sharper.”
Mr. Rockwell notes that Leica’s lenses, which are still assembled by hand in Germany, do not have the added features of modern DSLRs, like motors, and that the company uses the highest-grade glass available.
I agree with this.