When carriers release an OTA even if it is a new version of Android, there are many parts to the firmware besides just the OS itself. A firmware update aka the OTA generally updates everything from the device baseband radios (what lets you connect to cell towers for CDMA, GSM, LTE), the Kernel (which has the modules aka drivers for each hardware component such as GPU, Camera, Bluetooth, GPS, etc.., manages the file system, etc..), the OS itself aka 4.3 in this case, all of the pre-loaded applications and any customizations that Motorola has made. The first OTA always includes a fairly large list of improvements regardless of if there is a new version of Android included or not.
A few examples you typically see on the first OTA are battery life improvements, performance improvements, cell signal improvements, camera tweaks, etc..... Now that's not to say that any of the reported issues thus far will be fixed in the OTA as we really won't know till we actually get it, but it's safe to say that device manufacturers typically work to resolve the biggest most critical issues first. Now some of the issues can be quite complex so you get a hacked fix of sorts that improves things but doesn't fully resolve the issue till a 2nd or 3rd update down the road when they've had enough time to resolve things.