But the significance of the phenomenon (or whatever) to which the word referred must also play a part in the decision as to whether to store it up for posterity.

I've been thinking about this since I first read this thread...what if someone starts to read old newspaper articles in 20 years, for a research project, and needs to know what "dot-commer" means? Even if the word has fallen out of use, it is still useful to have recorded its meaning. Haven't you ever read a book with an archaic word and looked it up, and been (a) thrilled it was in the dictionary anyway, or (b) annoyed because it wasn't?