Well, the Silver one is not shipping right now due to a higher amount of orders. So that would be why it's not shipping, because there are none to ship at the moment.
No it's not higher demand than the black models. Apple is having a supply issue with the silver models.
That's why every single person on these forums that ordered a silver hasn't received it, but the higher demand matte and Jerry black are shopping earlier.
Come on Apple, make more silvers.