And more importantly, to allow a 30fps camera to run at 25fps to make it truly compatible with PAL standard TVs (and why this isn't already in every camera sold by default is a mystery to me). Some Powershots do run at 24fps or 25fps, so why not make it adjustable for those that run at a higher fps?
Its unfortunate that those that run at odd fps won't do 30fps. This must be due to a sensor limitation or clocking frequency limitation or something.
I believe there's a phase locked loop crystal divider that generates the framing information, this will have the appropriate division ratios programmed into it.