Everybody can use Skype. Why should I use Webex?
Skype can be used for same goals. Skype is often used for private reasons. Skype for Business only works within the UvA for the emplyees and (at this moment) it cannot be easily used with the people from other institutions.
Using Webex you can communicate with your working relations outside the UvA (colleagues, project partners, students) without mixing this with your or their private life. UvA has a licence for Webex and a contract about the security of data.