To be fair lemons are fairly expensive for what they are. 30p each or summat, for summat you eg squeeze over some fish for a sharp flavour. It's the same price for a whole bottle of malt vinegar. You can see how a squeeze of lemon over fish when you have fish and chips, for example, can seem "posher" than shaking vinegar over it all.
G&T: again, seems fairly wasteful to use a whole fruit just to flavour a few drinks. If I'm having plain gin with tonic I do like lemon in it. But if I have flavoured gin I just put ice in, no fruit. I guess the flavoured gin saves money. So to me, flavoured gin seems less "posh", since it doesn't need any additional ingredients.