I really don't think etiquette is any different now than in the past. What has changed is people now have more disposable income, are more mobile, and hence there are just plain more people in parks. On top of that, the people you meet in parks are more diverse than ever.
The concept of personal space is different depending upon where you are from. Rural people have different personal space boundaries than suburbanites. People from the city, who live in apartments and condominiums where all the green space is public just don't change their perceptions instantly when they enter a camping situation. They have lived all their lives in an environment where the land surrounding their homes is accessible to all. To expect them to suddenly realize that there are separate yards for each residence might be too great a leap, especially for children. You only know what you know.