As "acceptable" attire gets more and more casual, some organizations are almost forced into making some guidelines. Reading the article and hearing some examples, I can see why MLB had to do this.
I worked at a place one time where Fridays were casual - in other words jeans were okay. But one day the receptionist wore skin tight jean shorts, and the CEO then made it so all days were "business casual", including Fridays. That's what usually happens - some people think that dressing like they do when they go to the bars or club is okay at work as well, and it then causes a correction in the code towards a little more professional attire.
The corporate environment I'm in now is technically business casual M-Th, and casual on Fridays. But the human resources department has a fairly detailed guide about what is acceptable and what is not. People dress pretty casual around here on non-Fridays as well though, so the guidelines are not strictly enforced. And there is a degree of common sense - if it's snowing like crazy on Tuesday morning and you come in to the office in jeans, no one is going to get on your case about it.