Just back for HAL Ryndam cruise and had the pleasure of sailing on Diamond Princess in Dec 2007. We have a daughter with MS and have been looking at options of taking her and her family cruising some year, so I've been trying to scout out the issues ahead of time.
My observation is that on DP the cabin stewards used carts for their supplies; these carts took up half the width of the passageway while the stewards were working, which was mornings until about noon and then evenings also. It was very difficult for anyone with a wheelchair or walker to pass by the carts; possible if someone was there to help scoot the cart absolutely against the wall and if the wheelchair wasn't too wide.
On Ryndam cabin stewards didn't use carts and the passageways were always clear. SOO much easier for anyone trying to get by with a wheelchair or walker.
Hope this helps, and I'd be interested in anybody else's observations. Thanks, m--