Coursera takes off

Coursera has just announced that they hit three million students during March.  One year.  Three million students.  These students took over ten million courses.  Quick - do the math.  That's over three courses per student on average.  That would make me not so unusual for registering for ten:  I've completed three, am in the midst of five (two very half-heartedly), have abandoned one, and one more has just started.

I'd be very interested to see a breakdown of the geographic distribution of the students.  Certainly, I found the distribution in World History Since 1300 to be very broad and the students very diverse.

edX, the Harvard-MIT platform has far fewer courses, and far fewer students (in the thousands, not the millions as far as I can see).  Is there a critical mass factor in course selection?  Will more people 'shop' for courses, where there are more courses?  The bigger you are, the bigger you'll get?

As a frequent-flyer member of Coursera, so to speak, I'm certainly more likely to browse the courses there.  However, I did register for an edX course recently: Michael Sandel's famous Harvard course on Justice.