Factory scheduled maintenance are a series of services unique to each vehicle. It isn't a one size fit's all style service. These services help keep your vehicle running newer, longer. What might be required service on the neighbors truck at 30,000 miles might not be required service on your 30,000 mile sedan. In general these services might be viewed as preventative and are also usually items not readily seen. On a interference engine replacing a timing belt is much more affordable than replacing damaged heads or a engine - should the timing belt fail. Or routinely servicing differential fluid is much more affordable than replacing a differential assembly.