It's an investment
I'm an IT consultant specializing in Information Security. My laptop IS my job.
No one else supplies them to me or supports any problems I might have it it fails. So, I buy the beefiest MBP that isn't silly. (That means is will have a longer lifespan of usefulness - cpu speed, memory, etc.) I, get Apple Care. (It makes my repair plan 3 years.) At the end of three years, I buy a new one.
By then, the device may be a little "behind" in features and performance and might be a little worn (I do tend to take pretty good care of my devices even though they travel almost every day and every where.) Having a device that would render me "unemployed" for multiple days should it fail without a reasonable service plan would cost me about half the cost of the MBP. Over three years, the program works FOR ME. It might not apply to the casual user.
Beyond that, the questions need to be: Do you really NEED a MacBook PRO? or would a MacBook do just fine? For my work, the Pro is almost required. Do you NEED the latest model? Or would a more reasonably priced used or refurb of a previous model do just fine? To be honest, I'm looking at most of what I do and my 2.4C2D/4/500 is still doing really well at almost 3 years old.
mac-10