That was because they selected a different Sony image sensor to use. Canon makes and designs their own SLR image sensors. And it was done to use a lower noise sensor, where noise is a big issue for P&S cameras still unlike SLRs
A bit pointless to me. Low light performance of the G11/G12 is still unacceptable, and they've lost the enormous benefit of the 14.7mp sensor. I've used the G11 and went back to the G10 out of preference.