It is interesting to me as a technologist to remember these companies as both powerhouses in their domains and failing enterprises. What I don't know is what allows a company to successfully 're-invent' itself or to recover its core values and return to a previously powerful position. IBM did that once transitioning from PCs, Microsoft seems to have done it, and Apple pulled it off when Steve Jobs returned. SGI died, MIPS is nearly dead, Sun is dead, Compaq died, Dell might be considered a comeback, National Semiconductor died, AT&T Bell Labs died, Northern Telcom died, Polaroid died, Kodak is nearly dead.
There are obvious issues when the accountants take over and start squeezing the cash out of a company, and companies that just keep getting deeper and deeper into a technology that isn't going to survive when something new has come along. But why are these events so crippling that companies that have the resources to re-invent themselves seem to so often fail to do so?