Having been involved in some of the statistical analysis of product longevity data, one project involving a related LED technology, I can tell you that they have not actually tested their life span. Phatlight doesn't likely know, its estimated. The estimates are based on sophisticated statistical models which take into account actual known parameters, which have been measured. This makes the models relatively accurate.
For those familiar with statistics, you may also know that one potential pitfall in such models is that if you extrapolate out passed known ranges, the predicted values can be way off. If you utilized human growth characteristics for the first 10 years of life to extrapolate height and weight at 45 years, people would be 50 feet tall and 1000lbs. That isn't true because our height and weight from birth to adulthood is non-linear. The big difference is that much of this is known for devices like LED's, and so they are far more linear devices. Additionally, if we find that they do decay in a non-linear fashion (most bulbs do, but LED's are very different), we can account for that in the model and create more accurate predictions.
My understanding is that the specified life of the LED bulbs for these projectors is actually far less than what is being statistically predicted. LED's are known to dim very little over their life time compared with other bulbs, and we will not see them needing replacement every 2000 hours by any means. Getting 10,000 or 50,000 or even 100,000 hours is another story, I think we will see the low end, not the high end. Still, from even own look at the statistical data for the "related" devices, I'm fairly certain you won't see 50% loss in output at 50,000 hours, it will actually be more likely to just die than dim greatly.
Because of how they are currently being implemented, I am fairly certain they will be very expensive to replace. I'm sure these manufacturers are doing their best to make this as reasonable as possible, but its not going to be as simple as replacing the LED chip. An entire assembly including parts of the cooling components are going to be replaced, however the boards can be rebuild with new LED chips, as most of the other components will not age much.