In Wikipedia, if you compare different versions of pages, you can compare the versions to see, what has been changed. Now I can browse through versions, for example:
http://p2pu.org/en/groups/personal-learning-plan-do-it-together-university-the-independent-learner-in-community/content/the-presentation/history/

But I can not see what has changed. Of course I can open the versions in two different windows and compare them manually :-)