I'm pretty sure that the mime type setting is always your responsibility if you are just hosting files for downloading, you would handle it in your own download code controller, I do for both down and up loading
A file is just another object to the server, it does not matter what is in it, the mime type just tells the browser what the objects format is. So the simple answer is the server can host any file object, what you do with it and how you serve it is down to you.
Re Silverlight, suggest you read up......
http://goo.gl/iexiY