Grades

Does anybody know why there is the minimum grade for attending the coaching courses?  As said previously, there is a distinction between Aikido ability and coaching ability, and the coaching courses (rightly) focus on teaching ability.

Isn't it up to associations who they deem it appropriate to send on the courses?

It is a shame that there is not a standard across the board for Grades. I have certainly come across some "instructors" claiming various grades who's ability to perform techniques appears to be lacking. I have recently taken my Ikkyu grade and have to admit it was hard work. I wasn't entirely convinced I had actually done enough to be worth the grade but I guess that is often the case.
I dont know if I could coach effectively, I am regularly asked to demonstrate techniques in class and generally feel pretty uncomfortable when doing so.
I think there are natural coaches and those who will never be particularly comfortable with or good at coaching. Certainly length of time practising and grade should be a good indicator of an instructors ability. However I have seen aikidoka jumping from association to association and style to style in order to raise their grade particularly when they appear to be stuck at a certain level within a club, including moving to a position where they can effectively buy their senior grades.
How a standard could be managed/ policed is a difficult subject; perhaps individual associations would have to submit to BAB inspections and/ or representation at grading panels to ensure the standard? Not sure that would ever be agreed to - associations value their independance so much - but it is an interesting thought!