Unlike the other cults which were dependent on oral tradition or clumsy, expensive-to-house, and relatively user-unfriendly scrolls, Christianity is closely associated with "the book". Unlike an amorphous collection of scrolls or parchments a bound book has much less ambiguity about what is included and what is not in a particular gospel.
Did Christianity benefit from the same forces that MS Windows enjoyed as being at the ground floor of a rapidly growing technology?
Interesting that you should ask this. I don't think you can 'explain' the success of Christianity on the basis of the adoption of the codex, but I happen to be reading Frances Young's book "Biblical Exegesis and the Formation of Christian Culture", and it discusses the codex in particular.
Christians did what Jews would not: they took the OT texts and instead of keeping them in scrolls, they put them into codices. This was basically taking the 'sacred, revered text', and putting them in notepad form, the kind of thing used in schools and by accountants. As much as Christianity was a 'bookish' religion, in a sense it desacralised the book as object, and in fact emphasised the living message of those books.
Did the codex aid Christianity? Probably, the adoption of a new book technology certainly didn't hold it back. However, I don't see how you could make the argument that the codex explains Christianity's success.