The
people who say that sort of thing are more than likely only to have a vague and/or
superficial interest/
knowledge in
music and so would only have ever been exposed to the more
mainstream stuff being
produced at any one given time. This means effectively what they are saying is correct from their
point of view, but far from an
absolute truth. These people probably don't like
hip-hop either.
Mainstream pop music has indeed gone down hill since 'the good old days'. It is essentially the same as it was 40 years ago, albeit with minor production improvements and a bigger budget, but yet a lot more vapid and false. The differences between an late 80s/early 90s boy band and a late 90s/early 00s boy band are not big at all. A slicker production, more pertinent lingo and thats about it (oh yeah, their styling is different because fashion has changed). In the 60s and 70s, pop music was actually good. There were many successful singers, songwriters and producers who actually wrote excellent material. A Motown catalogue of that era would show a world of pop music that was actually good. Now it has become a lot more about catering to a demographic and has lost its heart; indeed it has become an industry just like any other, with marketing, not music, at its core. Back in the day the focus was on actually writing good songs to sell records, now they use P.R to sell them. You can tell this because people still love Micheal Jackson (his old stuff, that is, and not his personality either) but noone remembers any boy bands from 1993. Although the makeup and definition of mainstream pop world has admittedly broadened to include 'alternative' bands, many of these bands are still uninteresting and are manufactured in the same way as other boy bands. Sonically they may be different, but underlying them is the same market research and adveristing teams. I am not saying all mainstream (or what can be considered mainstream by some) music nowadays is bad, but just that the trend shows it is heading towards a vacuous demise.
However, in the realm of other music things are quite different, and this is were the statement falls into disrepute...
Where can I begin to write about all the brilliant things that have happened in music in the last 20, or even 10, years? The birth of ' electronic' music, whether you like it or not, has led to a completely different musical scene and there is a lot of great electronic music. The most interesting sounds are the ones that are pushing the envelope, and because of the unfortunate stagnation in the sounds people can produce on a guitar (don't get me wrong, it's not completely exhausted yet, just in a bit of a lull), much of the boundary exploring has been done by electronic artists. Once good sounds are discovered and used they are then snapped up by the mainstream that is looking for the next trend, but by that stage most of the excitement and energy is already somewhere else that is new and unchartered, leaving an empty, false version in the mainstream world. It then becomes so derivative it's not funny. However, people out there still continue to experiment and create brilliant music. Look at Aphex Twin, The Orb, 4 Hero, Talvin Singh or Squarepusher, and check out the Electronic Music Artists node for more info on good music.
But guitar-based music (by that I mean conventional instruments, singer, etc.) has by no means declined in this period. A lot of interesting, thought provoking and sonically blissful stuff has happened throughout this time. Highly influential stuff that has changed the way things are done and the way people think. In the last 20 years bands such as The Smiths, New Order, Sonic Youth (and their influence The Fall), The Pixies, Slint, Tortoise, (early) Metallica and many, many others have had a profound impact on the music of today.
Despite the many criticisms that people have about rap and hip hop, it is a valid form of expression that has undoubtedly been a huge influence on popular culture in recent years. This is both good and bad. Good in that new sounds have been put forth, spawning many fantastic musical trends, but bad in the way that 'Gangsta Kultcha' has taken over many a adolescent life (and wardrobe). Suburbia is not the ghetto. Or Da Hood. But apart from that the genre has put forth many interesting ideas and sonic creations. Fantastic and influential artists include Grandmaster Flash, N.W.A (real gansta-ass niggaz), De La Soul, (early) Wu-Tang Clan, Run-D.M.C (pioneers of the whole rap-rock crossover thang) and DJ Shadow, among others. A large part of pop music now is influenced by hip hop (i.e. good ideas leeched to death).
So... it can seen that there has been much great music in recent times (and I have mentioned but a meagre few examples), but of course, I guess in the end it's all relative. That's my two cents anyway.