I would imagine you are correct to assume this happens more in the hilly terain out west vs the flatlands of america where radar coverage is more limited. The track was "probably" all done ifr, but radar coverage only occured where there was tracking.
Radar coverage doesn't affect flight aware tracking. See http://discussions.flightaware.com/view ... hlight=mcb
On the nevada example, this is not to say he wasn't vfr on Departure or Approach, but explains to me the lack of track on departure and arrival. Otherwise, why would the guy file ifr just for their enroute phase?
The following is with the stipulation I haven't had a chance to gander at the airspace around the airports in question, but in a general sense....
There could be many reasons, one being VFR in the beginning of a flight, the airspace restrictions isn't as bad, such as dodging MOAs. VFR traffic can go through MOA's, where as IFR cannot IF the MOA is "hot". If it's cold, IFR can go through MOA's.
Looking at the altitude, on Damiross's flight, he maintained VFR altitudes which makes me think he wanted "VFR on top" which is much more flexible then a standard IFR flight. Plenty of discussions in the past about VFR on top as well. Since this flight does it so regularily, he could have a helping hand with ATC getting him in the system easily.
Having never done VFR on top, I don't think that traffic can go through a hot MOA since it is an IFR clearance, maybe somebody else can chime in.