It's a good question. But of course it have a lot of different opinions. Who says girls dont like to use skayp, we like and use it even more than boys, we just like to choose with whom to talk and with whom not ! 

possibly they have had bad experiences from pervert guys online , so they better be careful !

Most of my skype friends/tutors are female, so I disagree with your assertion. However, I will agree that skype is often bad, and deserves a spanking.

I use Skype every day with my Egyptian friends from this site, I give them a hand in English and sometimes I let them know what I was studying in my last lesson with my Pimsleur cds.  I don't Skype anymore with strange men, just not worth the aggravation.

Apart from what was already said, girls tend to feel more shy and insecure because of their foreign language speaking skills. At least, that's my observation.