Apple is also a member of Khronos - the highest level of membership in fact. Doesn't mean that they are at all interested in furthering and promoting the standards Khronos oversees. Microsoft is also a member of Khronos btw and they have been actively hostile towards open graphics standards for much longer. It simply makes sense for corporations to get access to relevant standards bodies in their fields, whether they are interested in adopting those standards or interested in competing with them.