I would say you should be comfortable riding alone or with your own group as there are long periods of time when you are not with anyone, or riding styles differ enough that you don't stay in contact long.
Good point. In addition to timing affecting how many people you run into, things like differing paces, daily schedules and lodging choices can, too. I have had several encounters--both on the road and in camp-- with people heading the same direction on both the Northern Tier and Trans Am routes and I can only think of three instances when I actually rode with someone for any length of time, and those three instances involved the same tandem couple.
Also keep in mind that some people may prefer limited interaction with others. I think it's important to recognize that preference and respect it.