Apparently those that don't complete service are second tier people, perhaps not allowed to vote at all, etc. It seems that's okay though, as Johnny's dad is a successful businessman and doesn't want his son to go into the service, so whatever is excluded to those with no service didn't change his mind on it. If anything it's hard to tell because the service seems to have a positive opinion among the young and those that are in it, but everyone else not so much.

The percentages are listed later in the book and this idea is expanded upon as well.