People have always sought out new, interesting things based on stimuli from their surroundings.
I think the ubiquity of the Internet has merely caused a decline in the importance of advertising. In the past, it was perhaps more important, but the Internet has made people more interconnected than ever before. It's easier to seek out like-minded people and find out their interests.
To put it simply, I believe the input of your "friends" is the dominant stimulus nowadays. This naturally encourages file sharing. The word of a friend alone may not be enough to cause you to spend money on something, but the threshold to download is much lower.
This kind of behaviour has the potential to expose you to a much greater amount of entertainment, as it's not limited by what the labels choose to advertise. Of course, it won't always lead to a sale, and many people will become freeloaders, but that is unavoidable.
I believe the only way to combat illegal downloading as a source of entertainment is to provide a legal solution that is both as easy to use as your favourite torrent tracker *and* price it so that the majority of people pay it for the sheer desire to be a law-abiding citizen.
As a personal anecdote, most of my books, games and DVDs I bought exactly because I had access to the material on the Internet. This includes many imports that would never be locally advertised.
The only exceptions are my PS3 games (minus a few shared PSN games). Even those I bought either after trying them myself or because I couldn't stand my friends going on about how awesome they were.