Many of these people have been in the music business for decades and at one time may have been major industry heavy weights and as such they know the business, have lot of contacts and favors they can call in if necessary.
The aspiring "Indie Artist" is in abundance and so, there's money to be made and it's a booming business for those with the knowledge and deep contacts. The aspiring Indie artist looking for advancement can be convinced to pay for and/or subscribe to some form of music based service. Don't forget the ever-increasing use of mobile apps.being used for music 'transmission.' I ventured into the app. world in January, 2013 and here I am in July with a much broader fanbase and fatter wallet thanks to my apps.
Now, having said that, I'll begin to talk about what an artist should be doing to earn from their music. Besides getting listeners to buy their songs from their website, iTunes or Amazon, you should be looking to get your music licensed. Music licensing is giving someone else permission to use your music in their work for a period of time without giving up your ownership of the music being licensed. This will generate long-term income which will be paid to you from whatever performing rights Organizations or P.R.O, you belong to (BMI, ASCAP, SESAC).The 1st thing you need to do is have music that can be licensed which is to say, your songs should sound like a finished product ready for market. That doesn't mean that you need to go out and get your songs professionally mixed and mastered, though that's not a bad idea if you can afford it, high quality home recordings are acceptable. It should be well produced, clear and available in (wav.) format even if it in mp3 format.
I believe many artists get caught up in the glitz of music making and focus only on making what they hear on the radio or music videos and for the indie artist that will not earn you anything much. Urban styles and music set the trends for what pop and fashion follow and like it or not the urban styles and music are being used to market to teens and young adults. So make the adjustment to include songs in your catalog that can earn money for you while in route to your other dream. That's just smart business in my opinion.
In closing, don't take your eye of the lesser-know music sites. Thay can (and have) turn out to be very lucrative.
Having music placements to your credit can have a twofold effect, the 1st being, if you a promoting yourself effectively, it can be a good talking point to include in your bio and it will show potential investors or A and R rep that may consider signing you that your music has proven value based on the placements it's received in various other formats (e.g. tv, movies, games, advertising campaign etc). And the 2nd, it shows that you are earning from your music and you're cable of putting a song together that can be marketed to the public.