Skype is already a Microsoft’s foregone conclusion, and Microsoft certainly will not give up such a great opportunity to deeply integrate Skype into Windows Phone, to create a feature that only they own while iOS and Android don’t have or insufficient.
Skype also supports iOS and Android platform, but for Windows Phone platform, they plans offer some unique features. To give people a feel of the application is no longer a mobile phone application but an integral part of Windows Phone. For iOS and Android, because they have limitation to third-party applications to use the mobile video processor and the phone book, thus making Skype impossible to do a similar integration.
Taken into account that one of the possible main purposes of Microsoft acquired Skype is to promote the combination of Skype and Windows Phone to highlight their own mobile operating system, then will they limit the use in terms of iOS and Android in future? Another point worth noting is currently the deep integration plan of Skype and Windows Phone also still remain at the draft stage, because the only other EU-related bodies officially approved the deal (perhaps before the end of the year), the real integrate action can be formal started.