I understand that there was a bit of a sea change 'around' 1998, but it's still a bit of an arbitrary cutoff. Really, it should be "up to '1997-ish'," with a description or list of the offending technological advancements that push something over the edge from retro to modern. Case in point, here are three bikes I own, from 1997, 1998 and 1999, which correspond to their years exactly opposite of what you'd expect. All were standard production models, hand made in the USA - but none of which is really appropriate for the forum:
Clearly, I like bikes from that specific period. I was preoccupied with kids and career at the time though, so it would also be interesting to hear more about the global forces (economic, technological, fashion, political, etc.) that caused things to change so drastically in such a quick period of time. Because it didn't last, either. Seems like the industry is going through a similar transition right now: long period of relative static and "refinement," followed by a brief period of rapid technological advancement and drastic changes in standards,.... leading to a period of economic struggle and brand consolidation. I think the bike industry it's own worst enemy when it tries too hard.