Honestly, since this is one of the years where both entrances to the internal routing for the rear brake are on the top of the top tube, if you'd told me that it was a drainage hole that they put a threaded collar on so that the edges wouldn't be stress risers, I would almost believe you. Almost, except for the fact that the internal cable routing is a complete tube within the top tube. Which reminds me, when I frame-savered the frame, I didn't spray any in those holes. Oh well, maybe next time.