is Device limited to mobile phone & purchasing apps? Because we sure as hell have 'Devices' in the house older than 2013 that came with those titles for free. On desktops & laptops. That's why OP's original question is still valid.
Do you mean the mobile apps are now finally free too? (know yer history son).
There's a few different things going on here with regards to the Mac versions.
Versions of iWork prior to 2011 were traditional boxed commercial products - as in, you went to the store and bought a disc. The Mac App Store had been introduced in 2010 and in 2011 Apple released iWork '09, the then most recent version, on the Mac App Store as three separate apps at $19.99 a piece (which meant that the three together were cheaper than the $79 they had been charging for the iWork DVD-ROM).
In October 2013 they released new versions of all three, now just called "iWork" with no particular year or version designation, and now exclusively on the Mac App Store. They also made this version a free upgrade for iWork '09 users both to reward existing owners but also because this allowed them to transition to using the Mac App Store as their central software update platform. At this time, however, they were still three $19.99 applications.
The way the free upgrade worked was that the Mac App Store looked to see if you had iWork '09 installed and if so it would install the newer iWork (leaving the old one intact) and associate your Apple ID account in the Mac App Store as having owned the apps. At the time there was a trick people discovered - by accident or design the Mac App Store was incapable of determining whether or not your copy of iWork '09 was the full version or the 30-day trial, which Apple had rescinded from their website but which was still floating around. If you installed iWork '09's trial and rebooted, the Mac App Store would start installing the new version of iWork and your account would now own the latest iWork even though you had not purchased iWork '09. In a statement, Apple acknowledged that this was possible but that they thought the convenience of upgrading and Mac App Store association was worth the potential loss in sales they might suffer as a result.
In October 2014 Apple announced that the three iWork apps would be free with new hardware purchases. Prior to this point you had to either qualify for the free iWork '09 upgrade or purchase the apps, and anyone who didn't do the trick above would still need to buy the apps.
What's changed today is that now the three iWork apps are outright free to everyone, not just people who bought a Mac after 2014 or were willing to perform the iWork '09 trial trick. If you had them on devices prior to 2013 for "free" then either you had taken advantage of some promotion or some bundling, or you may have gotten the upgrade as a result of the 2013 rollout.
The iOS versions of iWork followed a similar trajectory, though skipping the part about being on DVD prior to 2013 and any upgrade tricks - they were released as three $9.99 apps, free with hardware purchases past 2014, and now just free to anyone.