The Anthrocon staff probably chose that weekend unaware of the conflict it would have with SDCC, as www.comic-con.com still does not list the dates on it's site, and people doing business there were only informed on the last day.
Most of the people I know attend both - and now have to make a choice. Personally I had already written off Anthrocon as being too expensive a trip and was not planning to go again anyway, though martes may still want to go.
What this will really affect is CCD. Anthrocon will take away a lot of the attending members and put a serious crimp on the mini-convention.