Would you expect to get your Bachelor's degree while only making 2 out of the 24 classes your instructor teachers?Why should Aikido be any different? When you get an F in class you can't go to your teacher and say "Oh but I was reading the text book at home a WHOLE lot!!" The point is, you didn't make it to class enough to advance. Likewise, don't expect to advance in Aikido when you are absent from class."A" students show up to all their classes on time and complete the course work. Aikido is no different. It requires discipline, dedication and commitment. You have to give up time, money, other activities and some socialization to part-take seriously.
I think you may be overlooking the counter-argument that has been persisting in this thread. There is no denying that students should not be passed if they do not have the technical skills. However, utilizing your analogy, if I were to take that same class for for 12 years wouldn't I have developed the knowledge required to pass that class?
Is a person training twice a week for ten years going to be unable to attain the skill level of a person training three times a week for six years? I don't buy it. Yes, I agree that going once a week will make it harder for a student to remember what they've learned a present a major obstacle for most. However, I cannot accept that a focused and dedicated person attending classes twice a week would not be able to attain the same skill level as they would if training three or even four times a week. It would simply take them more "years" to put in the same hours to get there.
I am certainly not denying that going two times a week may not be enough for some students to make consistent progress. However, training four days a week may not be enough for someone else. Unless we are talking about a big gap between training sessions, I think it comes down to the individual.