I was struck by that - but I recall when we briefly had an AGA and my mother, in excitement, whisked us off off to an AGA shop, being earnestly told by the lady there that you could run an AGA very cheaply for as little as £1 per day (which, as my sister pointed out, meant it would cost you approx £400 per year). I wonder if gas cookers were seen as something of a luxury and thus the expense needed justification.