The desktop sharing of skype has a long way to go to be used seriously. I can only assume from your comment that you haven't used it. They may have their audio codec down, and the video codec works for live video, but not for content. It's the same deal with JPEG for text for instance.
Skype is strong in businesses. In the office-setting people first and foremost use the text-chat, then the audio calls, then the conference calls. Video calls come dead last. I wouldn't be surprised if even desktop sharing is used more than the video feature.