Just read an interesting article here that says some browsers are inferring semantics to the html when the display property is changed in CSS.
This seems to go against everything that CSS stands for in my opinion and although the consensus was that this is more a bug than by design as the css specs do not seem to indicate that there should be any semantic change to the html when css is applied.
There are some workarounds for accessibility mentioned in the article but I feel that if you want people to make accessible sites then you need it make it easier for them to do so and not harder. Also allowing css to affect the semantics of html is a slippery slope as you don’t know where it will lead and you can never be sure of anything ever again 