Why are LED bulbs not lasting 100,000 hours?

With the introduction of the LED bulb, one of the main selling points of this new form of lighting was the much higher lifetime rating. During the early days, residential LED bulbs had lifetime ratings of 50,000 hours or even 100,000 hours printed on the box. But as Hack a Day points out, if you browse the list of specifications of LED bulbs today, you'll be hard pressed to find a model that offers 25,000, most claim only 7,500 or 15,000 hours.

In a new article, Hack a Day tries to figure out what happened.

Certainly moving away from incandescent bulbs to more efficient lighting makes sense, but maybe we never really needed 100,000 hour bulbs in the first place. The lifetime of even 7,500-hour bulbs is long compared to the rapid pace of advance in lighting technology. Does it makes sense to buy expensive long-lived bulbs today, when better, cheaper, more efficient ones may be available in the near future?