More seriously, shows aren't arranged on a whim the weekend before. There are many constraints on the date chosen, and avoiding a single sporting event is just one of them (and, if we're honest, probably a fairly insignificant one in the grand scheme of things). I don't know when the 2007 Cup Final date was announced, but I suspect that the show date was at least provisionally selected before it happened. I don't know for sure; I wasn't involved with that side of things.
What I *can* say is that, with another (non RISC OS) hat on, we're selecting dates for this kind of thing over 12 months ahead and have to just hope that they don't clash with too many other things when the date arrives. That's how it works.