I agree with Vladimir. Most of the newer ships in the lines he mentioned have excellent access. And it should be noted that since no architectural guidelines exist, whatever the cruise lines are doing, they are doing voluntarily.
I usually end up inspecting all categories of accessible cabins whenever I'm on a ship to do story, and I've found that on the newer ships the bathrooms are all the same. They are "ready made" and they just plop them in there. This is good, because as at least it's consistent.
I have to say that I've encountered many more "Rube Goldberg" facilities at hotels than on cruise ships. I have seen some questionable access, but this is mainly on older and retrofitted ships. No not all ships are appropriate choices for wc users, but it's good that we have resources like this -- so people can share information so they can make the choice that is right for them. Different people have different access needs.
Editor, Emerging Horizons
The only accessible travel magazine.