I don't really get the difference in pricing for MyPassport PC and Mac. It's the same drive, the Mac version is slightly more expensive, but the PC version is compatible with usb 2.0 and usb 3.0 and the Mac version is not...
The thing is, not only will next Mac releases have usb 3.0 implented when Ivy bridges comes out but also Thunderbolt is on all Mac and coming rapidly to recent PC ultrabooks, WD hard drives or at least the MyPassport for Mac should be Thunderbolt ready and have the adequate slot.
Plus it makes MyPassport Studio clearly obsolete : nobody serious about Video/Graphic/Audio production and editing, and who uses a Mac, continues to use Firewire, which is clearly a dying interface. It really is about Thunderbolt and I hope the next WD will be compatible because it's going to be REALLY quickly adopted by users compared to eSata or even usb 3.0.
In short : make the next MyPassport for Mac (and PC is a safe bet) with a micro-usb 3 and a thunderbolt port (and they are about the same size).