Except the 4S is what, 9 months old now?
I'm not sure what you are trying to prove? First of all you were trying to claim the iPhone has never been available free on launch in the UK and now you are nit-picking over deals.
They cost more or less the same over 24 months and they are both good phones. There's no disputing the S3 is selling well in the UK so they are not discounting it because it's a failure.
I never understand why some Apple fans brag about their products costing a lot more than the opposition. I don't know about you but I'd rather pay a bit less for my next iPhone.