The difference is the webparts. A repeater webpart is different than a smart search webpart. So you might want to look at the underlying controls which make those webparts up to figure out how each work.
In this case upon inspecting the smart search results webpart, it is loading the a user control from /CMSModules/SmartSearch/Controls/SmartSearch.ascx. You might try setting it backwards like this:
srchResults.UniPagerControl = "pgUniPagerControl";
As I stated every webpart is different even though some use the same underlying user controls.