Dozens? Out of 39000 students? Even if there were many dozens this is a small percent of the total student base (390 = 1%).
The number of students cheating at higher institutions is frequently reported to be much higher. For instance:
http://chronicle.com/blogs/percolator/is-student-cheating-dr...
The problem is not Coursera. The problem is people who cheat. And I am not sure that this is much of a story at this level.