Why is it assumed that you can rub your chin and ask for a discount on one item but not the other?
Generally speaking I buy "last years" models. I expect a discount as the technology does evolve slowly. If I was buying at the time of year when the new stock was due I would expect a discount as other retailers, some on line would be discounting their stock. The retailer is quite within their rights to explain what added value they can add over others if you buy from them.
Besides the price tag is an "invitation to treat", you can make any offer you want and retailer can decide if he accepts or not.
It's very unlikely that anyone would take you seriously on small ticket items if you asked for a discount. If there is only 5p profit in a pint of milk then there's not much room to discount and not much of a loss if you lose a sale.
And to answer your original question I think No. Probably couldn't be bothered to deal with a fussy, needy, overbiked, short arse who wants discount on everything.