I'm not sure I'm reproducing your specific issue since it is somewhat map dependent, but have you tried going into Options - Acitivity Profile - Map Display Features and turning off everything under Points? Geographic features are there along with shopping, recreation, and on and on. The only one I keep toggled on is fuel.
I think the problem he's describing is the same that I have. The layers of the map lose detail as you zoom out, that is, at various zoom levels particular roads are removed from that layer.
I've always figured it is for clarity, more important in urban areas than rural. But, that is where the most Garmin customers are. In a dense area like a city if they didn't disappear there would be too much clutter to clearly see major roads.
In the sticks it is the reverse, you need to see that level of road detail against the bigger picture in order to plot a course that uses those roads. So, when you zoom out far enough to see the nearby town or highway the road you are on and those to the destination are no longer visible.
From what I've gathered in reading GPS forums this is by design. If there are options to select at what level certain roads disappear they are not available in Garmin's consumer level interface, and may not be available at all. Some say each level of zoom is a unique map and if it were decided to leave out certain roads beyond a certain level it likely isn't possible to switch them on and off.
If the Open Source maps allow the ability to have these roads included in more levels as you zoom out, the map file will probably be larger for the same amount of coverage area. So, it might have been a trade off for space in memory vs. detail. It could be that Garmin policy was determined in order for the North America map to remain within a certain file size.
Who knows why they did it? I just wish they had allowed the user more flexibility to fine tune it. I'm crossing my fingers that the Open Source Map project might offer a better option. Even if all I have is Texas and a few surrounding states in the same memory space that all of Garmin's North America now occupies. I can buy more memory easy enough.