There are a lot of people who probably already had their eyes on a shiny new video card, and view Bitcoin as a 'discount' off of the purchase price.

The math here is questionable as well, especially with summer heat and electricity costs factored in. Still, it's a psychological thing to convince yourself that you're going to get 10-30% 'off' your hardware purchase as long as you use it for bitcoin mining. Even worse is that you must buy now to get in on it.