That was the case at the beginning of the 20th Century when standards were low (have a look at the technique of some of the founding fathers if you can find them on film). When my original Karate teacher came to the U.K. in the early 60s, 5th Dan was the highest technical grade which he held, but as the art developed and evolved, further technical grades were added up to 8th Dan. 9th and 10th Dan are usually honorary grades and are bestowed for services to the art: promoting it, pushing up the standards, and model behaviour. These Dan grades are augmented by the ‘shogo’ honours, renshi, kyoshi and hanshi for which criteria differ amongst associations. Here’s an example:To the best of my knowledge 5th Dan is the highest rank that is attained by skill in the art. The ranks of 6th Dan and above are not attained by skill and are not awarded by an instructor but rather by your peers. It's your peers that promote you to 6th Dan and above and promotion at those ranks is given based on factors such as your teaching ability and how much you contribute to the art, not on your technical skill the way the lower ranks are. At least that's how it is with some styles such as the first style I started to seriously train in.