According to Digital Domain’s Press Release, Bob Katz confirmed that the latest version of iTunes (v11.1.1) makes iTunes Radio play all songs with the same perceived loudness and the listener has no control over. This has great implications.
The way to turn the loudness race around right now, is for every producer and mastering engineer to ask their clients if they have heard iTunes Radio. When they respond in the affirmative, the engineer/producer tells them they need to turn down the level of their song(s) to the standard level or iTunes Radio will do it for them—and not always in a pleasing way. iTunes radio will not just ‘turn down the volume,’ but may peak-limit the important transient peaks of the material and make the song sound ‘smaller’ and less clear than its competition.
In other words, more you compress your final master worse it will sound on iTunes Radio. This is a great news. Make sure you read the whole press release. It’s quite detailed. And if you want to learn more about the topic check out the Bob Katz’s book iTunes Music. I highly recommend it.