SilverSprite doesn't require XNA to be installed, but as for the rest, I would agree that Xbox is a major focus for XNA, and there are some good reasons you might not want to use it for Windows, like the fairly subtantial prerequisites. I don't feel, however,
that XNA for Windows gets shortchanged unless you want to use DX10 features in your game or integrate it into another application.
Just released an update to SilverSprite which addressed some of the most glaring things that were missing, like bitmap font support and being able to read compressed textures. The compressed texture one is pretty cool because if the compression looks ok
for your particular textures, it will compress to 4 times smaller at least, and possibly 8 times smaller. This then will compress even further in the xap compression so it can be a big size savings.
There were also some missing methods that have been implemented for more compatibility.
Finally I included the Farseer Physics demos shown in the video here to the solution, along with a version of the class library which makes it easier to use with Farseer.