To some degree it also depends on what OS being used and what settings the user has in Outpost:
I get more pop-ups on my XP pro system than on my win7 netbook and that is for the same program installations and updates, etc. All this despite having the same Outpost settings and customisations. Not that the greater number of pop-ups on the XP system, I still don't find them particularly intrusive.
Outpost also has the Simple interface in which the HIPS would probably be even less intrusive, so there are many things which avast can decide how to implement this licensing. Given that the avast firewall was specifically designed to keep user input requirement to a minimum, so I guess they would be looking at the same policy when integrating the Outpost license.