In a recent survey, a group of high school students was asked about their preference for using digital textbooks versus traditional printed textbooks. Out of the 100 students surveyed, 70 preferred digital textbooks, while 30 preferred printed books. The school principal stated, "Since the majority of students prefer digital textbooks, we should replace all printed textbooks with digital ones to meet students' needs."
Which of the following, if true, would most seriously weaken the principal's argument?