Well, he might not want to upgrade. He might want to keep his computer for a few years, then buy a whole new one. When you think about upgrading, its just a waste of money. Sure, your getting better performance, but your also throwing away the old parts that you paid for too. Unless you can resell them, it would be too much of a hastle to upgrade, especially the processor. Upgrading the video card is ok, if you didn't pay huge prices for it. Ram is ok too, since more ram never really hurts. But upgrading the cpu is really expensive, especially if you payed 150 dollars for the old one.
When you buy your computer parts, think to yourself. Will you ever upgrade? Will it be worth it in the future to upgrade? How much money wil you be willing to spend on the upgrade? Will you see a huge perfromance hike? Would building a new computer be more cost efficient than upgrading?
Think this through. Don't just go by what other people say because they want to upgrade. If you aren't planning on upgrading, socket 754 is a perfectly good choice. You can get better computer parts for less with socket 754, and can probably do fine with it for the next 2-4 yearsl. However, if you plan on spending money on upgrading in the near future(like withing 1-2 years), then get the 939.