I can't imagine the difference in weight will affect anyone. It'll be hand luggage or literally in your pocket. I've never had my hand luggage weighed.
£270 (£330 for the 3G model) for something which is essentially the same as a £110 device (it's laughable that anyone would pick up a Paperwhite and complain that it's too thick and/or heavy). Now that's a niche market.
I don't think this will sell very many, but I suspect its real purpose is to get people to consider buying a Voyage instead of a Paperwhite as they'll believe they're getting more of the cosmetic thrills of the Oasis without the stupid cost.