(i'd love to know the marketing reasons behind simply chucking over 40 years of company heritage in the bin for a new "shiny" name??)
It was a case of bits of the company splitting away and they couldn't both keep the same name so the measurement group had to come up with a different one. I think there was a similar story behind Agilent being created from HP when that happened.
As you say, same thing happened 15 years ago. The sad thing is that HP became run by money men and women who had no idea how to run a business consistently, always looking for short term monthly and quarterly gains, they thought that being an accountant or a "banker" was enough without having to have a clue about the business.
The HP brand today is junk, particularly after their EDS takeover and more recently the pissing contest with Autonomy, it's become a race to the bottom. This is quite unlike Agilent who managed to maintain their reputation, as I hope Keysight will.
I am no fan of rebranding, and find the continual supposed added value from the branding, M&A and strategy MBA wankers to be nothing short of money for old rope in almost all circumstances. I am sure I'll still be referring to Keysight and Agilent as HP for many years yet, keeping the memory of the good years, when reputation was everything, and the bean counters and bankers remained behind their desks and steered clear of the boardroom.