There are differences between an online environment and the physical classroom environment. As a university professor, I teach in both environments. A MOOC (or really any online course) is designed for an individual who is self-directed, motivated, driven, and organized. Someone who can manage their time and prioritize their needs. Is this an average 18-22 year old? No. Is there a small percentage of 18-22 y/o who would be successful taking MOOC's or online courses, yes...majority, no. Plus, so much is learned within a university/college context for those 18-22 y/o that has nothing to do with any "classroom" environment.
There is something important about being able to sit in a classroom of peers and think, discuss, question, process all of what is taking place organically, in the moment. Valuable learning opportunities. Online is far less organic and much more "staged" in many ways. It's less spontaneous and sometimes, though not always, the best learning happens in those spontaneous moments.
Learning is more than just the accumulation of information. It's also processing that information and figuring out where that piece of the puzzle fits in what is an ever expanding knowledge universe. It's context and collaboration. It's connection with that information in a meaningful way. For some a MOOC will accomplish this...but I am thinking probably more so with those who already have a great deal of experience and therefore already have that context.