Note that bulb life is affected by number of "firings" and misuse. For example, rapid switching on-and-off is bad. Also, not letting the machine go through the proper cool-down is also bad. It's very common for users to just hit the hard power-off switch, vs. the soft-off button which will run the fan for a while to cool the bulb.
I'm not saying you mis-used the projectors, but if you weren't the only one using them, this sort of mis-use is common and go a long way to reducing bulb life. If you watch the AV forums, people who actually know how to properly care for their units (unlike Joe Blow average user, not you but probably a lot of the other people who used the projectors you had to then maintain) and are the primary/sole users often get more than the rated life-expectancy out of their bulbs.