You just have to love SEC football
A lot of people dress up for all the games at UGA, not just homecoming. Of course, you will see folks with t-shirts and shorts on, too, but they're not in the majority.
I think it's easier for us, though, because nice clothes are easier to find in red and black than, say, purple and gold or bright blue and orange.
To answer your other question, Georgia has the Georgia Girls. Ditto on what everyone else has said about no hanky-panky and it being an honor. I think I just always assumed that there were these types of organizations everywhere. I learned something new today!