Keep in mind that Adams wrote Hitchhikers for BBC radio and it was first broadcast in 1978. This means that he developed it in ~1976 to 1977. The first Seiko digital wristwatch, the Astron, was released on Christmas 1969, and popular adoption can then be assumed to be ~1970+. So, for Adams, the digital watch was only 6-8 years old, still fairly new. I mention this, as it puts the quote in the context of the time. Adams meant that the digital wristwatch was an amazing thing still; such amazing precise time, so cheap, so small. And then Adams says that this amazing tech is just a pittance to the rest of the universe. It's typical British humor, but in a different way than we see it now.

So, when you say "People who wear watches as a status symbol wore elaborate mechanical ones, people that just needed time used their phones." you are wrong in the context of the time Adams was talking about. Digital was very much 'cool' back then, or at least not 'cheap' as we see it today. Also, no-one had a mobile in 1978, as they were first introduced in 1979 (and had no clock).

As for today, fashion works in cycles, and among hipsters the digital is 'in', but who really knows. We do know that the Casio F-91 is the watch of choice for IEDs and Casio admits that they sell "well" 25 years after introduction. I remember reading that the F-91 is a graduation 'gift'/shibboleth for IED school grads, but I can't find the source. I guess that earns a fair amount of street-cred or 'cool' in certain circles (of bastard child-killer terrorists). If you do see a group of people with a lot of old Casio F-91 watches, I really hope they are not company you keep!