When you ask for a facial tissue, do you ask for facial tissue or do you just say Kleenex sometimes, reguardless of wether it is actually Kleenex brand or not? This is actually fairly common to chose a name for a type of product as a generalization when reffering to an extremely similar product. Just like (I Think) has been mentioned, in certain areas of the south "A Coke" justy refferes to any type of soda, not just cola and not specifically CocaCola. Windex=Glass cleaner, etc.
Point taken. I always order Coke with my cheeseburgers when I mean cola, then have to assent (impatiently) to Pepsi being ok.
However, the use of a brand name for a generic name is a misnomer. The Coke/cola, Kleenex/tissue miscues are generations old & too late to fix, but we're here at the dawning of a new cone-type era. Why pass a practice of misidentification on just because it's been done before?