Top 40 music certainly goes through phases, doesn't it? I'll bet if I listed a few songs from the Top 10 in a particular year, you could probably make a reasonable guess as to what year it was to within a decade for sure. At the very least, try for "early" "mid" or "late" and a decade.
Let's try it shall we? How about Addicted to Love by Robert Palmer, Kyrie by Mister Mister, How Will I Know by Whitney Houston, Say You Say Me by Lionel Richie, and That's What Friends Are For by Dionne Warwick and Friends. Think you got it to within a few years? Here's the answer.
Let's try again. Take Me Home Country Roads by John Denver, Go Away Little Girl by Donnie Osmond, It's Too Late/I Feel The Earth Move by Carol King, Maggie May by Rod Stewart, and Joy To The World by Three Dog Night. Got it? Check to find out.
One more time. Livin La Vida Loca by Rickie Martin, Every Morning by Sugar Ray, Genie In A Bottle by Christina Aguilera, ...Baby One More Time by Brittany Spears, and Believe by Cher. How did you do?
The point is not to test your trivia. The point is to try and look at patterns of how pop music changes. There's a certain sound to 60s rock and top 40 that defines it, and the same goes for the examples I used above. Compare the five artists in each example. Their music is not the same, but there are certainly similarities. This is as much a business phenomenon as a musical one.
When an artist releases some music that is a bit different than the mainstream, and has a huge hit all of a sudden, it can signal a change in direction. Every record company is going to look for artists already on their roster to see who has a sound similar to this "new big thing" and if they have no one they'll recruit new artists. Within a few months of some groundbreaking hit with a new groove, there'll be a dozen similar acts on your radio. Money talks.
That's why buying music in this age of easily available free music is an important choice. Consider it a vote. With each purchase of a CD or iTunes single, you're telling record companies your opinion. You're telling them what music you like, and you are backing it up with money. Will someone else download different music for free? Sure. Does it count as much to the creators and publishers of music. How can it? While they may be able to track freely downloaded songs and use it to get a picture of the musical landscape, there's no money there, and the massive success of iTunes means that there's a money trail to follow instead. If you owned a record company, which trail would you follow? Consumers who tell you what music they like with their dollar, or those who don't?