The up front cost is cheaper than a plasma or LCD but in the long run you may spend as much. The lamps in those things last no more than 3,000 hours and can cost up to $500.
True, but consider that 3000 hours is what, 3-4 years of viewing pleasure! 
And by that time, it'll be time to upgrade again to a better, cheaper projector. 

Plasma and LCD TV's are just too expensive right now. And, they are still just TV's.  Using a projector is the only way to get that "Home Theatre" experience.