While I didn't recognize most of the songs on KPWR's playlist (if it didn't make to Billboard's top 10 pop charts between December 1991 and December 1997 when I lost access to that information), I think your analysis sounds just about right. Keep in mind that there is a (roughly) 20- to 30-year gap between the time when a song is on the regular playlist as a hit and the time that it shows up on that same playlist as an oldie. I noticed this during the 1970s when I was a child and teenager and 1950s music (as well as such TV sitcoms as "Happy Days,") were the rage. That trend continued through the 1980s and began to fall off during the 1990s. We saw that happen with the 1960s during the 1980s and 1990s as well. The only decade that didn't have as much remembrance thus far (at least according to radio station playlists) was the 1970s, possibly because of the dominance of AC during that period (though 1970s music is still being played on many oldies and classic hits stations today).
And *all* of this fits in with what K.M. Richards and Michael Hagerty have discussed in other threads; namely the age of the audience advertisers are trying to reach (usually 25-54 years) and how radio stations are trying desperately to reach that age group in order to remain profitable.
My advice? Don't worry! I expect we will be seeing more classic hip-hop stations showing up on radio dials in the not-too-distant future, especially in cities with large black and Latino populations. One place where I was surprised to see a classic hip-hop format is Missoula, MT--KHKM-FM at 98.7 mHz is trying the format for now and we'll see if it catches on with a (mostly) white audience as it did back in the day.