There have been some issues in the past, and it has differed with different versions of some device drivers. For mass: and host: it is quite common to remove any leading backslash of the path string before calling the device driver functions. But uLE strives to present a consistent user interface, even if this sometimes hides some underlying details of the driver functionality. That is why we always present root devices with a '/' after the colon, and always separate the drive spec colon from the path with '/', in both cases representing the root folder level of that drive.
On a side note, I was wondering if the first [/] after the [:] is ever explicitly needed by any functions in libmc/fileXio/fileio/etc.? I've heard that including it might actually be incompatible with some file handling functions, but I haven't run across any that had trouble, as far as I know.