There is also the possibility that Microsoft didn't get their end right they did it with samba and some networking.
I don't think so. drivehq.com, a cloud storage company, proposes WebDAV for end-users. The same WebDAV URL can be used in Win, Mac and Linux.
Possibility 1: Microsoft, Apple, Linux community developers and drivehq.com all did the WebDAV implementation wrong but still manage to maintain the inter-operability using the same URL
Possibility 2: Microsoft, Apple, Linux community developers and drivehq.com all implement WebDAV correctly.
By Occam's razor principle, possibility 2 is more likely.