It depends upon how you treat it. Laptops are designed to be move around, but still moving them around a lot could eventually cause problems. The most likely part to go first is the hard drive, as they have a moving head and if it crashes the hard drive could be damaged.

If your laptop stays in one place then it most likely should give you years of use.

Corporations tend to refresh their laptops every three or four years. Usually, they buy them with a three year warranty and once the warranty expires feel the need to upgrade. They continue to improve and change their software, so often need newer hardware. Microsoft pushes the latest OS and since their latest OS's often require upgraded hardware they sometimes have no choice.

Consumers on the other hand, often have simpler needs. Browse the web, e-mail and typing letters or simple spreadsheet. They will often get many years use of a refurbished laptop, as their needs do not change that quickly.