The 'F' in GF5 means it's got no viewfinder, hence is rather more diminutive size. The 16MP sensor in the G3 is really no worse than the ones in newer cameras, and the AF speed is already plenty fast so there's no great gain with a newer model. Basically you can spend a lot more money for not much more camera, and at ~£250 the G3 is a right bargain.
Ah, OK. That makes sense about the model numbers. I'm not disagreeing with you about the G3 being a bargain, by the way. I only chose the GF5 as an example because it was linked to on one of the pages you showed me. Ta very much.