Although they may not have an outright 4-year plan, students are going to think of college when planning their summers. Now, not every single student will, but those who want a future will at least to do something to make their applications look good. Furthermore, they will spend summers earning volunteer hours, but they may want to glorify it a bit by volunteering overseas, for example, to impress.
Do students choose summer activities to look good on applications? I agree that some do, ones who are driven to succeed in school or career, whether driven by themselves or by their parents. An argument can be made that this is justified for students who want to be admitted to excellent schools and to hard to achieve professions. A society that interviews families for elite preschools shortly after the prospective preschooler is born, will see a certain percentage of high school graduates in Summer jobs on Wall Street the week after they walk across the stage to accept their high school diplomas. But not every young person lives in that environment. Such behavior makes the headlines or at least sticks in our memories. I do not think is representative of the country as a whole.
No, not all students choose summer activities simply to look good on college applications. While some certainly do, to imply that all students do so is a bit silly. Many students choose their summer activities based on their interests and hobbies, not just for the eyes of college admissions counselors.