last.fm issued a press release saying its "free music boosts CD and download sales"...which makes you wonder how bad CD sales would be without all those free streaming services.

Yes, free music looks to improve music purchases, but be careful how you word the claim. Just being free won't do it. It's the type of free service that matters. (You have to dig into the press release to see co-founder Martin Stiksel relate the type of service to the sales.)

last.fm claims its sales of CDs and downloads through Amazon.com have increased 119% since its free-on-demand service was launched in January.

The bottom line here is people like on-demand streaming services more than non-interactive streaming services. Why? Because people aren't nearly as adventurous as is usually thought. They like running across new artists from time to time, but they'll take a sure thing over online radio's crap shoot any day of the week. They like familiarity with the occasional out-of-left-field discovery. Those early-adopter types that lust for fresh songs represent just a small slice of the bell curve.

If the music is not on-demand, people are going to run across their favorite songs less frequently. What are people more likely to buy: An unknown song that was picked by an algorithm or a song the user already likes enough to select personally? It's got to be the latter. There's a good portion of the 119% increase.

Part of the increase comes from a rise in last.fm subscribers. The company says existing users purchased 66% more music after the on-demand service launched.