Although many articles in English Wikipedia are perfectly accessible on Braille displays, some are not. In particular, the use of w:Unicode symbols often causes problems for Braille displays, and for some less-capable speech synthesizers. Ironically, the Wikipedia articles about the various forms of Braille itself are inaccessible in this way because they frequently use Braille Unicode patterns to illustrate their examples.
At the very least, it would be nice to put versions of the Braille articles (w:Chinese Braille, w:Japanese Braille etc) that use ASCII braille instead of Unicode symbols. I expect other articles could benefit from having Braille-optimized versions too.
Additionally, w:Grade 2 braille written by hand is better than Grade 2 braille generated by machine. For example, consider this word: chemotherapy. An automatic Braille generator might notice that this contains "mother", and construct it as che + mother + apy, which is totally unclear (someone writing Grade 2 braille manually would not construct the word in this way). Granted, many Braille generators nowadays don't fall down on that particular example, but there are others. Much the same rationale behind having audio recordings of Wikipedia articles instead of relying on speech synthesis, can also be applied to having Braille versions instead of relying on automatic conversion.