Gee, you're a pedant. Am I going to have to start opening Windows calculator every time I want to point something out?
Honestly, it doesn't sound like a joke, more like you're making fun of people who got less than they hoped for when purchasing a product. It doesn't matter if it's a graphics card or a car, false advertising is false advertising (assuming this is all more than a few misbehaving cards, of course).
Say you buy 1kg of *insert favorite nourishment here*. Wouldn't you get pissed if you found out it was actually only 0,8kg? Same principle.
Please don't misunderstand me, everybody says something that sounds stupid occasionally. That doesn't mean the person is stupid and pointing something out is not generally meant as an insult.