Great post!
I think he would have gone into much greater detail about the birth process if there was something miraculous about that. Just as the Apostles would have gone into detail about it. They knew Mary. I think it might have come up in conversation.
But these are written, that you may believe that Jesus is the Christ, the Son of God: and that believing, you may have life in his name.
-- John 20:30-31
The Gospels exist to lead man to Salvation through Christ. Everything else is extraneous; however, that doesn't mean it didn't happen, it simply means that knowledge of it wasn't deemed necessary for OUR Salvation.
The inherent fallacy of sola scriptura (at least to my way of thinking) is the notion that if something isn't mentioned in the Bible, then it isn't true. Yes, everything in scripture is true, but that doesn't mean that everything not in there is false.