I'd absolutely recommend watching Alec's video, but that's not a half-bad summary of the main point.

Think about it hard enough and it does make sense that for something as cheap and easy to produce as a light bulb, it stands that the consumer and manufacturers alike stand to benefit from a shorter, but more energy/cost efficient implementation, than a longer-lived, but significantly less efficient/more costly version in general use.

Edit - Though it should be pointed out that this is a rare instance of corporate interests lining up with the best interests of the majority of consumers, not something that happens very often, so you could see why people (even myself) would be drawn to believing a more nefarious reason for the 1000 hour lifespan if you didn't know the technical details.