I do not know, but I suspect this is exactly why RMS dislikes SAAS: because it can technically obey a license without having to give users the freedoms he designed the GPL to give.
The GPL isn't really about sharing source code; that's just a means to an end. The GPL is about being able to exercise complete control over - and having complete knowledge of - all the software that you use. To an approximation, SAAS is about the opposite of that.