Just to stir the mud a little more, the G12 will sync without using HSS at 1/4000th although for some odd reason not with the ST-E2 where it's a little slower. It's left me wondering the kind of shutter the G1X is going to have, focal plane as per the NEX or electronic like the G12.
Does the G1X have a focal plane shutter? My guess based on the above is no - a 1/4000 sync speed means electronic 'curtains'.
I used to have a Sony compact that also synced at 1/1000s and froze action like nothing else. I understand how the shutter of an SLR works, but I have never thought of what the negative sides to an electronic "curtain" is? Can someone fill me in? Why doesn't the slr's use electronic "curtains"? You could still have the mirror and everything, right?
I'm sure others will provide more detail on this but I believe it has to do with the sensor type. The G12 has a CCD sensor while the Canon SLRs have CMOS sensors. From all I know there are pros and cons to both types but what you describe is one difference where it's easier to accomplish different behaviors in one way or another.
Leaf shutters like on medium format cameras would be another option to increase sync speed.
In any case, neither have anything to do with freezing action since you can do that even at slow shutter speeds. Things like high speed sync (or high shutter sync speeds) are more important to control ambient light.
From what I understand, despite the myriad benefits of CMOS, one of their drawbacks compared to CCD is a more substantial internal capacitance that lets data "leak" into the pipeline after the sensor is turned off. This "leak" effect is not necessarily the same for all frequencies (colors of light), so there can be a color cast if using an electronic shutter with a CMOS sensor, which is why it's not done on DSLRs. A very frequent symptom of embedded systems implemented with CMOS ICs is a gradual, rather than instantaneous, turning off when the power switch is flipped (even if the switch is fully mechanical!), and if my interpretation is correct that lag in turning off is the reason that electronic shutters are a bad idea on CMOS sensors, which are in many other respects a better choice than CCDs for cameras.