Canon still includes examples with pellicle mirrors in some of their patents, and they haven't released one for many years. Many patents are filed to protect a technology and prevent someone doing something clever with it.
Companies are often blind to inventors ideas, the company I worked for turned down a patent by a employee that covered a method to deal with the Y2K situation. They signed over the rights to him, and he had it patented. When it became a very popular solution, he popped up with his patent and cleaned up.