I think that artists are just over-valuing what a play should be wortth. Most of the time when people play a song, they aren't even actively listening to it. It's just background noise. They might listen to 100 songs a day. At that rate, a month of songs would be about 3000 songs. For the $10 you pay, that only adds up to $0.003 per play. That's without even accounting for costs to run Spotify. So even if you raised the price to $30 a month, you still aren't going to get a singificant amount of money going to the artist.
Spotify opens up a whole new market of people paying for music. Before Spotify came around, I spent close to $0 on music. Because it just didn't make sense to me to buy music. My tastes change over time, very few CDs had a significant number of tracks that were worth listening to over and over again. Now I spend money every month, artists get some money, but only as much as makes sense. For the few CDs I did buy, I've played them hundreds of times and the artists have probably made less per play than they do on my spotify subscriptions.