I think on default the real-time scanners aren't configured to do the deep heorustic scans and whatnot - it's prolly not configured for full scan (archives etc.) to save time. I'd say run a manual scan once a week with everything enabled, see if that finds anything.
I never found a need to run a real-time scanner at home. I don't install a bunch of crap like a moron so I can avoid it. Once a week full-detail scan and it never picks up a thing. Maybe once in a blue moon.