There are several 'schools of thought' regarding this issue. I agree with what you are saying Mutley regarding running in line with SL, and the fact that kids/parents don't want to stand about in the freezing cold! I for one don't have a preference purely because of the hard ground at this time of year, if we had the resources to water pitch's then it would be summer rugby all the way for me
But if I had to choose I would go for summer, this is because I think a lot of kids are lost to rugby league because of the weather. I have seen it happen before, when the 'new boy' turns up and even though he shows a bit of promise, coach's don't want to risk them in the middle so stick them on the wing, 'new boy' stands there for 30/40 mins, in pouring rain or freezing cold, only gets to touch the ball once (if he's lucky), and then thinks 'i'll stick to soccer!'
We are lucky to have indoor facility's, but as you say Mutley, you can only do so much rugby coaching indoor!
If we went to summer we would also attract a lot more Soccer players, who once they have played may well get hooked and bin the softy's game
But only my opinion