'Groundies' are not allowed to wear coveralls when wandering around the station (or Tesco's for that matter) so why should aircrew be treated different.
To be pedantic there is a difference, coveralls are not a order of uniform - flying suits are - no14 dress if my very trivial memory serves me correctly.
That said, I don't really care. As long as we can do our function - the projection of air power - the rest is trivia. Does this issue effect the product?