Anyone know why Apple SuperDrives only work on Macs without built in optical drives?

This is something I have never been able to figure out. Apple is known for using cheap optical drives, yet their stand-alone drives don't work in a Mac with a built in optical drive, working or failed. The only reason I can immediately come up with is because they prefer to charge someone to replace it, but that seems a bit cynical. I just can't get my mind around how stupid this is, at least on the surface...