How and why did they get it before it was released here igor? Leaked
Priming the pump perhaps (all of the download sites), in preparation of an official release. The
http://www.avast.com/release-history page still shows 8.0.1489 as the current version.
Since as Igor said "I think it fixes compatibility problems with Windows 8.1." If this build number .1492 is only for win 8.1 (preview ?) there wouldn't be that huge numbers avast user with win 8.1 preview. It would make sense that new installations of avast have the latest version and those with it installed would have an in place update.
We saw what happened in the recent VPS update that was trying to cater for win8.1 some BSODs resulting in an avast emergency update.