Both Me and the Mrs got GAP insurance with ours. Those of you who got it cheap may have been offered the lesser cover.
There are two types, 'return to invoice' and 'shortfall protection'. I am unsure as to the in's and out's, but we both got the better of the two. I got a little knocked off the car value but paid £300, Mrs got less knocked off the car but paid £225 for her cover.
Its swings and roundabouts. Different dealers, and even just at different times of month/year the salesmen will be targetted on different margins, so prices will vary but will balance out.