Its not exactly a good thing that they leveraged itunes library vendor lock-in to drive market share early on. The anti-consumer aspects of their closed ecosystem directly resulted in their success. There's no doubt about it.
iTunes library (at least for Books and Music) is DRM-free and has been from an early stage (though _did_ launch with DRM).
I've had great success in migrating my purchased items back and forth from linux with absolutely no issue. However now they're using streaming and I'm unable to easily "own" any music anymore... or at the very least it takes you off of the easy path.
iTunes has been DRM free for more than a decade now.
Thanks for clarifying.