Presumably, the
labels are responsible, not Apple. Apple represents Apple's interests, while the labels are supposed to represent the artists'. Though in practice, the labels probably represent their own.
So, presumably, the labels have decided that offering their content for free to Apple for 3 months will result in more revenue in the future, just as Apple has. Surely any artist understands the idea of giving away their music in order to build a paying fan base in the future.
Ultimately, any artists who lose a significant chunk of income due to these 3-month trials and never see increased income after the trials should be upset with their label's failure to represent them well.
Then again, isn't that to be expected as an artist? Your label encourages you to give CDs away, or tour at a loss, and sometimes it pays off and sometimes it doesn't? Isn't this the same idea? It sounds to me like a worthwhile risk. How many people were going to buy your debut album or come see a show and choose not to because they used their iTunes streaming account? Versus how many people easily stream (and pay for) you music 3 months later because they got hooked on iTunes streaming?