Everything is slowing down, people are getting device overload and have limited disposable income. I have so many stupid devices that I have to label cords for when I move stuff. You can only own so many laptops, phones, desktops, tablets, etc. The tablet market isn't even fully developed and it's about to be deluged.
I have a great desktop that I won't need to upgrade for a long time unless there is a significant reason to do so. Same story with my laptop. With application developers split on where they're putting their resources we're not seeing many reasons or constraints that would require a hardware upgrade either.