Does brighter = shorter life?

I've noticed that some LED's are advertised aa having a 10,000+ hour projected lifespan, while others are advertised at 100,000+ hours. That's a huge difference.
What is the reason for this? Are the better LED's always 100,000 hours or is it dependent on their brightness? What are the Luxeons rated?

You've got a couple of things happening.

1) Marketers don't always get the numbers right
2) The more you drive an LED over it's factory recommended specs, the less lifespan it has. However, marketers don't care about this and usually put the factory specs on the package anyway.

In the real world (as opposed to the Marketer's world) no LED in a light will last as long as the factory states simply because all LED flashlights (with only 1 or 2 exceptions) drive the LEDs beyond factory specs.

The chances of you actually wearing out the LED before you wear out the whole flashlight is somewhere between slim and none, so I wouldn't even pay attention to the LED lifespan numbers anyway...