'Why?' 'Because we can.'

I don't know why the film creators decided not to be ambiguous like the book. It seems as if they were playing with the drug angle because the film shows Dale Coba's company as biochemical company (scene in which Joanna's car passes corporate offices at the end).

In the book the men tell Joanna that Bobbie will prove that she is human by cutting her hand. The scene leaves off at that with the men waiting outside Bobbie's house.

In the book, Joanna is taken by the men to Bobbie's house. They tell her that Bobbie will prove she is human and the robot idea is all nonsense. The t.v. is turned up very loud upstairs so the kids can't hear what is about to happen. The men wait outside on the porch. Bobbie is going to kill Joanna. The men stand out there and talk. "What is taking so long?" Next thing we see is the new robot Joanna. She no longer has any interest in photography, telling the new resident in town, "There is just so much to do around the house." There is much more storyline about the new woman, Ruthanne - the black woman. In the film we only see her arguing with her husband in the supermarket. In the book, she had become friends with Joanna until Joanna was changed, just as Joanna had been friends with Bobbie before she was changed. In the end of the book, Ruthanne's husband tells her he doesn't mind her taking time away from him for her writing. After all, they are going away for the weekend soon. He knows she will soon be a robot and not interested in writing anymore. He is able to bide his time. This is why Walter told Joanna that the men's association will accept women in 6 months or so. Was never going to happen. He was just placating her until they got the robot ready to take her place. Say anything to keep it all calm temporarily.