While the official Yosemite Park government website is inexplicably shut down, seems to me that it would take more effort to put up a "we are shut down" page than it would to just leave it up. But that's what you get when people are trying to make themselves seem necessary instead of actually doing the right thing.
Anyway luckily we still have the private sector and Yosemite.com is alive and well if you are looking for info on the park.
I do feel bad for people who have trips planned to parks during this time but if they are anything like me I would be finding a way in anyway. It is a park after all, wide open land that is always open.