I must admit that I'm having a bit of trouble understanding all of this, so feel free to correct me if I'm wrong. It seems as if Microsoft has launched a set of tools that enables developers of server software to distribute their software in a simple manner to users of Windows Server releases.
As far as I see it, it works like this. A developers gets his application in the new "store", dubbed the Web App Gallery. Users of Windows who use the newly released Microsoft Web Platform can then install the application easily, with the Web Platform taking care of installing and configuring the necessary dependencies such as IIS, as well as setting up the system properly.
The Web App Gallery is currently populated by ten popular open source server tools, which may seem strange for Microsoft, but Lauren Cooney, group product manager for Web Platform and Standards at Microsoft, says things are changing at Microsoft. The motto of her group is "Make Web not war". As she explains: "Essentially, what we have launched with Windows Web Application Gallery is a marketing and distribution pipeline. So if a developer has a great app they want to include in the Web Application Gallery, we will market that worldwide - so they have the reach that they never had before."
This is a new direction for Microsoft, and is a further sign that slowly but surely, the company is learning to work with open source, instead of against it.