Same here... there are several years between the technology used in these sensors, and the RX100 sensor is significantly larger too.
I believe Thierry had problems with the VR in his RX100 which drove him to the G15. I shot images in a cathedral in Ghent 2 days ago in very dark situations and am amazed at the quality I could get out of the RX100.
Besides, the problems I have had with my G10 (loose element in lens/sensor module) and S90 (quick death following extremely light water exposure) and the way Canon proposed to handle them from a cost standpoint has convinced me that their compact cameras were not a credible option, at least in Japan. Hope Thierry will be luckier with his G15.
Let me explain some things
I've had a G10 for 4 years and NO PROBLEMS with it, so really happy, except for noise above ISO200 :-)
And I still have a S90 with an early problem, but no more trouble after it was repaired.
Let me explain why I find the G15 better than the RX100 in most situations.
The response is the lens which is far more luminous
as soon as you are above 28mm.
So yes if you shoot mostly at 28mm, the RX100 is really better, especially at high ISO.
But as soon as you zoom, the G15 becomes interresting especially with it's excellent optical stabilizer.
Shooting here in winter requires more light.
Of course, I keep the RX100 (whole lens replaced, but Optical stabilizer still not good) for summer