If airplanes are built to last 30 to 20 years, why not cars?

[elleng]

8. Planned obsolescence

Planned obsolescence or built-in obsolescence[1] in industrial design is a policy of planning or designing a product with a limited useful life, so it will become obsolete, that is, unfashionable or no longer functional after a certain period of time.[1] Planned obsolescence has potential benefits for a producer because to obtain continuing use of the product the consumer is under pressure to purchase again, whether from the same manufacturer (a replacement part or a newer model), or from a competitor which might also rely on planned obsolescence.[1]

For an industry, planned obsolescence stimulates demand by encouraging purchasers to buy sooner if they still want a functioning product. Planned obsolescence is common in many different products, including but not limited to wheeled can openers, screws, ear phones, ear buds, shoes, automobile batteries, and bicycle tires. There is however the potential backlash of consumers who learn that the manufacturer invested money to make the product obsolete faster; such consumers might turn to a producer (if any exists) that offers a more durable alternative.

Estimates of planned obsolescence can influence a company's decisions about product engineering. Therefore, the company can use the least expensive components that satisfy product lifetime projections. Such decisions are part of a broader discipline known as value engineering.

http://en.wikipedia.org/wiki/Planned_obsolescence