There are very few militaries that don't have uniform and appearance standards and regulations.
Of course, every military has regulations of some sort. However, the the actual regulations itself and the amount with which they are enforced tend to differ. Not only that, but aside from the times we did see certain regulations enforced, we've also seen a large amount of cases where strange or unpractical haircuts and improper uniforms have been allowed in Starfleet. As such, ascribing the regulations of a current-day military to Starfleet seems a bit strange.