I've only skimmed it, but it seems like they're implying that "Intellectual Need" (emphasis on intellectual, as opposed to social or economic needs) is the only possible way to meaningfully motivate students. I see their point that it might be argued as one of the most effective ways to motivate students, but it seems to me like it's unrealistic to expect this "Need" to always be present, and is a trivialization of a more complex situation.

Academic motivation is a force caused by a wide range of internal and external factors, which people experience in different quantities at different times. Sometimes, you are in a course simply because you are obligated to be there and you do well because you need it to accomplish a long-term goal. Sometimes, you are solving a course problem because you find it intellectually stimulating. Sometimes, you give up on a problem because you believe you cannot succeed. Sometimes, you are simply unmotivated because you are tired and don't want to deal with stuff anymore. The MUSIC model of academic motivation [1] suggests a number of factors involved in the process.

Of course, I don't want to sound entirely dismissive - I definitely see the value in ensuring students perceive the "need" to solve a problem, and it's undoubtedly fantastic for an instructor to create that perception. I just wanted to voice that there's more to motivation than just the one avenue, and that's not necessarily a bad thing.

[1] http://www.themusicmodel.com/