I don't think you're quite correct here. It may depend on the firm, but most of the professions are pretty conservative. If you want to work in a boutique law firm defending tree huggers for protesting, then you can probably get away with meeting your clients in jeans and a tie-died T-shirt. However, if you want to succeed in an upscale Bay Street firm, then you probably don't want to show up wearing an off the rack suit you got on special at Moores. Furthermore, all lawyers have to wear robes and collars in court and yes, that dress standard is enforced. QCs tend to wear silk robes, because it's expected, not because they have to. Similar standards also apply to other professions and not because their colleagues are telling them, but because their clients expect it. I was once referred to a civilian medical specialist and after the first appointment I reported back to the Base Hospital that I would not see them again because I felt they were unprofessional (granted, based more on the condition of their office than their clothing) and, therefore, I doubted their competence.
We wear uniforms in the military in order to avoid shooting the wrong guys by mistake, but the reasons for our tradition of spit and polish has more to do with health. Leaders in centuries past may not have known why forcing their soldiers to meticulously clean and polish their kit and maintain grooming standards made for healthier, more effective troops, they just knew it did. Even today, if you have a soldier who can't master keeping his uniform clean and can't seem to shave and get his hair cut, how effective is he at other more important tasks?