Off hand, the costs of GPL'd software are not hidden at all. R for instance
demands that a would be user sit down and learn the language. This in turn
pushes a user into learning more about statistics than the simple overview
that Stat 1 presents a student.
In contrast, any program that simplifies use also tends to encourage a
simplified understanding. So, I believe it can be legitimately argued that
the real hidden costs lurk in "easy to use" software, especially commeercial
software with GUI interfaces.
JDougherty