Android 4.4 OTA system update hangs on Nexus 7 (2013)
The issue is solved. AFAICU, there was possibly a problem with Android update hosting site or somewhere on a trace to it, because the device was connected to and was capable of browsing Internet without a problem, including google.com. After some time, even without updating the progress indicator, the device displayed Install &amp; Reboot button. After this all goes well. So, the answers are:


Android provides cumulative update to 4.4.2, at least for Nexus 7 (2013).
Android should improve the way how it shows status information. If it encounters some problems with downloading an update, it should output something like "Connection timeout, trying to reconnect..." instead of just "Downloading" all the time. Also the progress indicator may have a bug preventing it from proper UI update in similar sitations.