The sad part is that most schools, institutions of higher learning, and informed business will want to keep the machines for a lot longer than 2 years. From a consumer standpoint . . . sure, spend $999 now and then spend another grand in 2 years when your machine starts to show age.
In a budget conscience environment like a school or university, where you're spending more for the software anyhow, you can't justify dropping $999 for 2GB of RAM and a dual core chip then try to upgrade to whole new system in a few years.