Well who said a tech conference is a "workplace"? I thought it was just a place where people who code hung out and discussed stuff.
What is "professional" and what is not depends on what you are trying to do. I guess I just don't think of a tech conference as equivalent to another day in the company cube farm, unless of course I am representing the company is some official capacity.
I can see an argument as to why that is a double standard, but it is what it is and if you are going to be a professional you have to respect that.