I could be wrong but I believe part of the reason is to prevent people from using PLE for non-learing activities. ie. anything you make in PLE can't be opened with any other programs, including Maya. I
If you make something with Maya PLE, I wouldn't be able to open the file with my version, Maya 8.5.
Don't be satisfied with what you can do but rather strive to do the things you can't do!
Exceed Expectations!