The Pulse audio API was never intended to be used by applications. They were supposed to continue using the ALSA API, so that Skype would work with or without Pulse audio. If Pulse is present, a correctly written ALSA-using application (mostly) can use it. If Pulse is absent, an ALSA-using app is happy. By contrast, a Pulse-using app can only work if Pulse is present & working. I don't know who within the Skype team made this decision, but it was the wrong decision. Skype could use Pulse just like any other desktop Linux audio app if they had used ALSA; instead they made it so that Skype cannot be used on systems without Pulse.