Like most of these polls, the results are skewed by the manner in which the question is asked.
The word "Need" implies that the AMA is essential to the activity of model aviation. Put another way, would model aviation exist without the AMA? I think it probably would but on a much smaller scale. There are plenty of countries around the world where modeling is pursued without benefit of the AMA or similar organizations.
Furthermore, by asking if "WE" need the AMA confuses the question further by not defining who "We" is. Some of us get more benefit from our membership in the AMA than others. Modelers living in Muncie benefit to a greater degree than those living elsewhere. RC modelers get more benefit from the AMA insurance than rubber power modelers or control line modelers. Competition focused modelers benefit from sanctioned events that the sport modeler does not. Ones sense of "NEED" depends on their chosen activity.
So do ALL modelers NEED the AMA? Probably not. Should we support the AMA regardless of our modeling interest, for the benefits they offer to overall modeling activities in this country? I vote yes.