Even though the iWork for Mac & iWork for iOS apps now share similar file formats & user interfaces, they are separate programs created for separate operating systems. Activating a new iOS device after September 1 gets you the iOS versions of iWork & iLife. Purchasing a new OS X device after October 1 entitles you to the free OS X apps. The same goes for the previous versions of the iOS apps. You can then install the apps on all of your devices with the same OS using your same Apple ID. BUT, getting the apps for one operating system does not get you the same apps for the other OS.
The update is available for those using iWork '09. If you have never previously purchased iWork ’09 and have not bought a new Mac since October 1, you will have to purchase the applications. You must have Mavericks installed to get the OS X updates.