I don’t see what more issues there would be apart from formatting for Macs. I own several Macs (and PCs) and My Passports/My Books. The drives just need to be formatted for Macs (with HFS) or, even better, with ExFAT so that they can be accessed on both platforms. The software itself can be downloaded from WD’s site. There is nothing Mac-specific on the drives themselves that couldn’t be found elsewhere (both WD Drive utilities and WD Security for Mac can be downloaded from the WD site).
Point being, if the “Mac” version is more expensive there is really no reason why it should be bought as it has no benefits over the regular version whatsoever (unless the user doesn’t know how to format the drive for HFS/ExFAT).