The reason for the receipt is to insure the voter that his vote was recorded properly in the first place.
And so that you understand the process, the voting machine would also need to have an internal printer to duplicate the recording of the vote.
One of the biggest problems with the electronic machines is that they lose their memory when being transported from the polling place to where the "ballots" are counted. (Ever have a cell phone die on you?)
Having an internal audit tape would allow the Board of Elections the opportunity to make sure all votes get counted.
It's not a question so much of the physical receipt but a backup should the machine fail after the vote but prior to it being counted.
For those who understand no explanation is needed, ...For those who don't none will.