I agree with you that it seems to be an odd thing to do but you need to consider the purpose of the server. As the theory goes, the congressional members that have been targeted have been provided Blackberry phones that sync up with the server, updating the database on a continuous basis. Therefore, as it's an ongoing operation there needs to be a place to store the server(s) and the incoming data outside of the capital. The data from the Blackberries is most likely synced up with a laptop in the congressional library and the Rayburn building where a laptop belonging to Imran was discovered.
The physical location of the server is important and if you were stealing sensitive data from congress you would want to store the server someplace that's at an arms length. The Sprayer street address works well as if the servers were discovered it might buy the culprits time to escape and it would be possible to frame the tenant of the property instead.
Once the authorities have the linked computer, it should be an open and shut case; lock em up and throw away the key. What about the clown, or traitor, who gave them access?
To me "shed" isn't a secure or particularly suitable site for electronic equipment, a matter of understanding of terms I'm thinking. Different countries and different vernacular.