Computers will be a different animal in as little as 1-2 years. What you're buying now is basically the end of Intel's current architecture and CPU lineup. They're coming out with a new set this year, with processors that won't work with the motherboard in your laptop. In 3 years time, the current CPUs will still be available and cheap... the question is if Apple will provide and install them for you as an upgrade.
Hmm so for work, I should go for the cheapest option for a laptop, because I may need to get another one next year? Whoopie.