That's ridiculous. Celebrities receive a mountain of emails, most of which are repeats of the same question, comment or request. In that context, requiring them to reply personally to every one is unreasonable.
Of course personal responses are not 'required', like you say they receive a mountain of emails. What you're saying is that rather than respond with a completely acceptable boilerplate email explaining that they get too much correspondence to write a personalized response, or allow an assistant to explain that and respond in their stead, they should deceive their biggest fans--the people who care enough to actually reach out to them, pretending that they did read and personally respond, which is an outright lie.
Requiring personal replies is ridiculous, yes. Doesn't that make faking them even more so?