As I beleive I said in my original post, I too have no particular problems with rank being awarded without exam. In fact has some have hinted at, often (too often for me) by the time the testee steps on the grading mat the certificate is practically printed. In otherwords allowing someone to grade is effectively awarding the grade.
Having said that though I return to my ancillary point that in an environment without formal competition (which *many* aikidoka train in) gradings are useful barometers of how we adjust to stress. You say you've never found a grading even a little stressful? Good for you, you must realise this puts you in a minority. Everyone I know feels differently. We can argue back and forth about how much stress is involved or if there is a better way to generate it but it's irrelevant. Unless I want to abandon my organisation (and I don't)this is the tool I have. And it's useful. I know this because in the past I've felt my technique was not my best in a grading, and I've watched my students techniques deteriorate at a grading. Which makes for a useful teaching tool.