Terry,
You have just articulated the very reason that we feel comfortable in providing extended time for students with disabilities who need it. In spite of what SEEMS to be the logical conclusion (that everyone would do better if they had more time), that really isn't the case. For those without disabilities, either you know the info or you don't. For students with disabilities that interfere with either their processing time or their response mechanism, extra time is necessary to assure equal access.
Dr. Jane Jarrow