A little off topic as far the Hottest 100 goes but here's a personal observation from the mid 90s.
When the big recording companies (Sony, Warners, BMG, etc.) cut their budgets for new acts, they issued "remastered/unplugged" CDs from major acts from the 70s and 80s. The likes of Led Zeppelin, Pink Floyd and Rolling Stones to name a few.
Many teenagers I knew listened to these when they first came out (obviously influenced by the parents' taste). Their knowledge of the then current music was sadly zilch.
It's funny how some people keep up to date buying new cars, iPods, androids and other gadgets, but when it comes to music, they are stuck in a time warp.