Russia announced that they were planning to end their involvement with the ISS in 2009 or so. This is nothing new. They've been telegraphing their displeasure with the ISS program for half a decade or more, and their lack of willingness to continue with it past 2020. The portions they're sending up to the ISS will be detached and converted in to a separate space station shortly after 2020. This is not "news", this is "established fact". Maybe it's more noteworthy the second time that they publish this through official channels?
The ISS will be a 20 year old international experiment at that point, yes the US and Russian halves of the ISS share a common "atmosphere" but mechanically they're completely separate space stations capable of detaching at any time. Most of the Russian segment of the ISS is made from leftovers from their MIR 2 project. It's no surprise that they're wanting to separate from the ISS. Those space station modules have a finite lifespan and most of them will be nearing their operational limits around 2020, with a maximum lifespan of 2030. Either we replace them with new modules or deorbit the whole thing. Russia has decided to replace them with new modules and go their own separate way. They've been talking about this for a looong time. The ESA has been talking about teaming up with the Russians moving forward, rather than NASA on the next space station. China ended up building their own space station after being turned down by the Americans. We're not making a whole lot of friends in the aerospace field with the ISS these days. The New ISS may be everyone - (minus) America next time around, due to our overwhelming fear of sharing orbital technology with the Chinese (who aren't allowed inside NASA buildings, just ask any Chinese aerospace engineer).