That's what I pay club fees for. And that is perfectly ok...
Actually Michael, here I have to disagree somewhat. I would take the view that you're actually paying to train in aikido. The work involved in getting a student up to a particular grade is extra (sometimes even superfluous) to this as it normally involves meeting artificial criteria - the grade itself.
Where I would agree with you on gradings is if the teacher forced you to grade - even indirectly by having a bar on "too deadly techniques below this level" nonsense - then yes it is open to claims of mere money making.
Note: I'm not defending the huge expenses some seem to claim for gradings, but a token to cover time spent and the extra bureaucracy involved (not always covered by the annual fees, certainly ours barely covers student insurance, equipment replacement costs and first-aid training for instructors).