Carol,
Are you saying that you NEVER turn your computer off? If you follow the line of reasoning, then you should never turn off ANY power equipment because it will last longer. Don't ever turn off the lights? Never turn off the TV? I'd love to see your power bill. I agree, don't shut it down every time you walk away, but there is some middle ground...
Although it is generally considered correct that some electrical equipment such as lights and computers may sustain more "total hours" if left on, it may not be that they will sustain more "usable hours" if kept on constantly. If the computer is not used for 12 hours of the day, at night for example, won't you get more usable hours if it's turned off during that time. We have a few 7 and 8 year old computers at the office that are turned off every night and weekend and run 10 hours each day. If nothing else, I believe there's no need to use or be charged for the power.
By the way, if you could post a link to the 100 year old light bulb that would be great. What type of filament is being used.
Hope this helps.
Grif