It depends how complex your markup is. I've found that a site that's been developed for the desktop can usually be made much more accessible by offering a diff

It depends how complex your markup is. I've found that a site that's been developed for the desktop can usually be made much more accessible by offering a different stylesheet. I.e. it's better than the alternative of doing nothing ;) But I agree - it's not always as straightforward as you might hope would be. Sometimes it makes sense to serve different markup.