I'm not sure if this would apply in your case, but I was recently checking DLP lamp prices and noticed the prices have dropped quite a bit since I last remember (at least for the specific Panasonic model I was looking at). This applies moreso when you're buying the entire lamp assembly and not just the bulb.
My guess is that most people with these older units are simply buying a new LCD/plasma set since their prices have really nosedived in the past 12 months.