4.3 isn't even a big change, either.
Here the way I see it.
(Major refresh).(Major changes, and big and small features that affect hardware).(Bug fixes, and minor new features that generally affect UI)
Example: 4.2.1-4.2.2: Essentially a new camera application, and the ability to hold down the WiFi quick toggle to go to the WiFi settings, among other small improvements.
Tapped from my Nexus 10.1