Traditionally there was only a limited amount of movement around on the knees - nothing like the amount that is done today.
If you watch Ueshiba in 1935, or even when he was older, he actually doesn't cover all that much ground on his knees.
Also, if you've done it, there's a big difference between moving on your knees on plain tatami (which is what everybody used to have) and the modern canvas or vinyl covered versions.
I don't know what you mean abt. traditionally and amount done today. What I do know is those who practiced it in the long distant past obviously did a lot of it but as I said they had a use and real reason for it. Maybe many nowadays don't know why they do it but just do as theiy're told.
In the old 1935 film of Ueshiba I would say he covers quite a lot of ground quite freely but obviously the gait is not as wide as could be if standing but there again doesn't need to be, especially when done by him.
Of course today the mats are much softer and that's all good as far as I'm concerned but perspective is the key once again. The old days of Japan didn't have cushion filled mats and trained specifically for terrain. Tatami actually would be harder than most grassy terrain.
But I did find it interesting once when reading how the guards of the shogun or daimyo etc. indoors trained in open hand moving from the knees as part of their job.
As I tried to explain in my earlier post the secret is moving from centre, turning around centre etc. This is what protects the knees. When done properly all 'weight' goes to centre and thus none is left on the knees.