Capt Midnight - The Multicom was designed to keep low level circuit chat off the area frequency and not to be monitored en-route, where for the reasons you suggest it is best to monitor area.
Creamy - ref the NOTAMs, have a look at the ICAO Annex 15 to see the requirements. There are additional Oz requirments also. I did not suggest that you don't check the NOTAMs, but checking the FIR NOTAMS can take some time and the direct relevance to a GA flight is often zero, hence I suggest that many GA pilots might not check them very often. Sure you can ask for a NOTAM on Farmer Joe's strip for a fly-in, but I think you will find that the details might be distributed by Joe. Such a NOTAM will only be in the FIR list unless it is very close to a published location or navaid, which is not often the case.
cheers