How often is "normal" for DLP HDTV bulb replacement?


I've just finished replacing my Mitsubishi DLP's bulb for the 4th time in 5 years this weekend. At $200 a pop, it's becoming less economical to keep this TV running than to go out and buy a new one with some features I've been wanting. Is there something wrong with DLP TV's in general that they have bulbs go out constantly? Grrrrrrrr
I have a Sony 46 inch DLP and have replaced the lamp once in 6 years. Last time I purchased a replacement lamp (no housing) off eBay and only cost about $80.
We've had to replace our bulb twice in 4 years. I have a friend who hasn't had to replace a bulb yet in their 4 year old TV yet. I've read numerous complaints on other forums too and it seems like bulb replacement varies more by manufacture than anything being faulty on your TV. Cutthecable is right, go to eBay for bulbs they're much cheaper there.