Did you miss the part of my last post in which I said that it had to do with some of the new standards they implemented?
The interface just felt cheap and like it was designed by a 12 year old, but what really annoyed me about it was that they were trying to FORCE everybody to design apps for their much-hated Windows 8 metro interface, which I found annoying and very unintuitive. They also stopped supporting XNA and tried to get everybody to make games with DirectX directly, instead of providing a decent game programming library.
Really, I just hate Microsoft's decisions lately, because they ditched a great engine (XNA), revamped an OS that made it 10X worse than anything before it, and then tried to force everyone to design apps for something they didn't want to. Not exactly the way to run a business.
But anyway, I imagine it was also a lot easier to support older version of VS out of the box because TGC still had to secure their rights to the licenses and APIs of VS2013, hence the delay of the support.
Meh game development blaugh!