I'm always amused by assertions that there are no longer rules for men's dress. After all, the man making that statement is never wearing a skirt, pajamas, or some form of what the English call native dress. In fact, in San Francisco he will probably be decked out in a shirt, cotton trousers and black duck-billed shoes just like the largest portion of the random people that walk by any downtown street corner.
So of course we have rules. It's just that they are mostly unstated, only loosely enforced, and vary according to the group a man finds himself in (which itself can change a couple times during the course of a day). As example I give you the current job interview practice which is to call ahead and ask what the locals are wearing so the candidate can dress to fit into the culture.
That rules still exist was confirmed to me the other day at a large (perhaps 2,000 people) event where the women wore cocktail attire. There was no specified dress code and yet the men, a cultural cross-section whose only commonality was a willingness to spend $100 for a ticket, were dressed almost uniformly in jackets and trousers.
That was interesting as well as unexpected because those men could have dressed any way they wanted and still gained admission. And I was glad to see confirmation that, at some level, rules still exist.