The 100 hour doesnt apply so much, but direct view do age the same way. It would be cool to see a half life rating for direct view tvs.
Like any other display device the lifespan is GREATLY lengthened if properly adjusted. Id say that an average 36 inch tube would last 8 years with a good image. Of course Im pulling these numbers out of the air, but based on my experience.
Have you ever been to your relatives house that have an old console tv? The image looks like all the color has been sucked out of it. It still works great but all those years of torch mode have killed the phospers.