What use is a messenging service if the people I want to talk to don't use it?
That's the problem they're trying to fix. With so many competing services that aren't interoperable you'll find more and more people that you can't talk to.
It's 2012. We've had instant internet messaging for well over a decade and the major providers still haven't agreed on a common, interoperable platform. Jabber was supposed to be it, and Google signed onto it, but everyone else is still maintaining their own API and platform. They all provide SDKs so others can latch onto them, and you can find a plethora of programs that sign onto all the major services unifying it on the user's desktop, but that user still has to maintain a separate account with each of the services, and the unification should happen on the internet, not on the user's device.
Skype has everything MSN live has, and most importantly, it has more users in more countries. Many - and probably most - people who have MSN live also have a skype account already, so it will only be a tough transition for some, and while some smaller portion of those will swear off microsoft altogether it's not going to make a huge impact.
And, of course, the reason they don't agree to a common standard is because they can't add new features easily enough. Yeah, email is universal, but there are no new features for decades, and it's riddled with problems (authentication, security, privacy, etc) and these aren't ever going to be fixed. HTML has finally gotten to version 5, but there's still significant friction regarding advanced features such as media content playback.
There's pain enough to go around.
