So my question is, why didn't they put a single 300W lamp in their 4000U PJ, insead of the 170W lamp?
See, now you are gonna make me get all technical...
Noise, lamp cost, and image accuracy.
A lower wattage lamp won't have as much brightness fall off over time which means that the color accuracy of the projector will stay closer of time. A brighter projector, in a critical situation, should be color balanced every couple hundred hours or so to maintain proper accuracy, while a HT projector can go far longer because the lamp color isn't shifting and the brightness isn't dropping as quickly.
The less bright lamps tend to cost less to produce with the brighter lamps running upwards of $300 regularly, while 170W models often running closer to $200.
NOISE! I think that is a big one. A brighter lamp is a hotter lamp which requires more fans and more fan noise, or at the very least, more size to muffle the sound. All of which adds to the price.
I remember getting my PT-L300U from Panasonic and the first thing I did was take it into Myer-Emco and putting it right above a Runco 720p projector. The image quality was a bit better on the projector which did cost $10,000 more, but the Panasonic couldn't even be heard when the Runco was on. In fact, to hear the Panny when the Runco was on you had to put your ear about 1" from the exhaust fan of the Panny.
These big projectors we are talking about here all would need a projection booth to house them. Something most people don't have the luxury of owning.
I will say that I've considered getting a very bright projector and if I did get one, it would have been located in a storage room and projected into the room I was viewing from to diminish noise.
