This is the basic conclusion I have come to based on my studies of this topic. The question you are asking, however, seems a bit different than the question I will be answering. The question I answer is, how many hours will this device function for? In truth, how long it takes to get to that time probably doesn't have a significant impact on how long it will last for, but there are exceptions.
The first thing I -always- recommend looking at is the warranty of a product, that variable will basically rule out the product lasting less than as long as the product theoretically could last. The epson 8100 has organic LCD panels. I have read various lengths of time for how long these panels last, the normal I hear is somewhere between 2000 and 3000 when the panels begin to fade, bleach or go out. The cause of this effect is the heat and ultraviolet light coming from the bulb or lamp itself. It is theoretical that a DLP projector would last longer on the aspect that it does not use organic LCD panels. A DLP projector has a spinning wheel inside that does not fade over time. The difference is a moving part. If the wheel inside of a DLP projector goes out, the projector is pretty close to busted unless it is repaired, I don't know what sort of cost this comes to out of warranty, but I do know that if the LCD panels go out on a LCD projector the cost of repairing or replacing it costs at least half of the cost of the item.
Generally, I'd imagine a well taken care of projector, LCD or DLP may last in the 4000-12000 hour range. This is assuming that it is maintained with care as you suggest and it also depends on how picky you are with the color of your projector.
A projector was this past September, http://www.projectorcentral.com/vivi...tor_review.htm
. It is truly revolutionary. Instead of a spinning wheel it uses lasers and LEDs to create the light. It is also driven by LED for the bulb. This gives the projector an estimated 20,000 hour lamp life. I suspect that this will become the mainstream in the next 2-5 years. One key aspect here is that, as this review states, this sort of dlp projector is very much unlike the ones in the entry level cost range. Thanks to the removal of this spinning wheel, the rainbow effect (RBE) is effectively eliminated as it would be a wheel speed of around 20x (most projectors go from 3-6x)!
Something that you may be interested in, inorganic LCD projectors. They are supposed to last much longer than inorganic LCD projectors.