You might feel that way, but many retailers and buyers will disagree with you. A grey camera will be worth less (or perhaps not even considered for purchase) by some.
Try and sell a grey item to
MPB, for example.
Have a look on eBay at what a Canon 650D will realise compared to what a Canon T4i will. Exact same camera, same specs, but unlike others where a seller might try and conceal the origins they can't do so.
To take it a step further, you will normally make slightly more money for an item with the original receipt (again, theoretically it shouldn't add anything to value but does), as it gives the item more provenance.