I think it's thee missing option in the updates menu. (And it is missing to fully control avast's update behaviour.)
Whether a common user would really care, I don't know. In fact I don't know if a common user has a look at the settings menu at all. But it would maybe be confusing if a common user finds that option too, because he does not know that avast is checking for updates after each reboot no matter when the last update was, and so he maybe would not understand what the option is for or that he will disable that "reboot-update" (which is good for common users) if using that new option... There you are right.
So maybe it would be better to have an option named "Avast looks for updates after each start of your PC (recommended)" [default: checked] in conjunction with "auto update interval".
I was annoyed because of that. So I wanted to know how many people would like to get that feature too and if there is a chance to get it (although I think there are not that many people missing it.)