Without the likes of gamestation on the high street the supermarkets wouldnt be that cheap either. I dont think they are cheap now anyway, not like when they used to sell new releases for £29.
I dont mind gamestation as the staff generally are chatty about games usually have better preowned games. Game however the staff hang around together, usually have no clue what they are on about and charge a fortune for games. Some of the preowned prices are a joke too.
Well, Tesco seem to be pretty good with pricing - roughly £5 below the price in Game, most of the time. I find the likes of Sainsburys and Morrisons are high/on par though.
I still think there will be price wars though - you'll always have the likes of Amazon and Play to compete with.
As for staff - well, again as others have said, I often know what I want and why - so have no need of talking to them other than "just this please", "no I don't want a rewards card thank you", "no thanks, I only want to buy this game" etc.... and besides, we have access to the internet and player reviews/release schedules - I cannot see (other than a bit of a chat) what staff offer.