Depends on your perspective really. Countless different PC configurations will all run the same games. Yet some people spend more than others, or upgrade sooner than others. They do it because they like shiny visuals, high-resolutions, and stable frame rates. The existence of older or less powerful hardware doesn't appear to be limiting the appeal of new products hitting the market.
I won't be buying at launch. But I get it. There's an opportunity to sell a new product to the people who thought the Xbox 360 and PS3 lasted too long, without alienating the people who don't want to upgrade their hardware every few years.