Android 4.3 for Nexusów officially been made available over the air system a few days ago, but still does not appear to each user be prompted for updates. You belong to the group of users who have not yet been officially treated to upgrade? Here is the answer why this is so. As explained in (apparently pissed continuous questions) Jean-Baptise Queru, an employee of Google:

OTA Updates accident occur very slowly. The aim is to detect catastrophic failures, which could not be detected by standard tests. These things happen, unfortunately. Since the start of Phase sharing have to wait two days to gather enough information to begin the second phase. Phase to make such updates to help stop the process when something goes wrong, because there is nothing to talk about a date when everyone will get the update.

Fortunately, there is nothing to worry about sharing phase OTA in Google counts not months or weeks or days. Maybe in a few days anyone can easily install Android 4.3 on a dedicated device. How many of you are already using Android 4.3 on your Nexus installed through official channels? Source: Google