The new update has some other improvements including being able to see when someone is typing a message to you, and the usual general improvements and bug fixes. But, the main change is with the login. The change log says it is an effort to make signing in easier, and those signing up for Skype for the first time will have to use their Microsoft account as well. There is also an option for two-step authentication as well, if you really need security.
There's no indication whether or not this same change will be coming to Android or iOS though. It makes sense that this change would come to Windows Phone, and maybe even other Windows products, because those require Microsoft accounts in general. Changing this functionality on other platforms gets trickier, but it certainly isn't out of the question.
Download: Skype for Windows Phone