I'm not sure what the grandparent was implying, but there's definitely a major benefit for larger screen sizes, even for those that are completely blind. iOS voiceover and other accessibility UI affordances are much more difficult to implement on the watch form factor, where a very small amount of content can be 'active' at a time.
There are some interesting startups targeting the possibilities here, but right now, smart watches provide a less capable experience for everyone right now.
