We understand why HC cost more then the MMPB. But that model fails when applied to eBooks. And eBook in a given format is still the same regardless of what versions are printed in paper. So why not just price it at the final end price and be done with it? The eBook is not going to change it's container.
Another peeve on the pricing of eBooks is that when an eBook is priced to fllow the HC price and the HC then becomes a MMPB a lot of eBooks don't reflect this change and then become more expensive then the current MMPB edition which makes it too expensive.