The a) "he" shouldn't be responding at all or b) the response should come from someone else's account.
The fact that he doesn't "sign" his email - to me, and to most, doesn't matter. He is the face of apple. His email address is the voice of Apple. When an email comes in from sjobs@apple.com - it's coming from the CEO. Because if they don't want it that way - or it shouldn't be interpreted that way - they should remove sjobs@apple.com and/or have an email address that doesn't use his name. That's my opinion as a Marketing and PR specialist for over 20 years.
Why should it come from someone else's account when people write to sjobs@apple.com, and not to ceo@apple.com? And why would people write to CEO, and not to sales@, service@, support@, press@ or whatever?
If I write to sjobs@apple.com asking: "Steve, do you like burger or steak better?", and he would reply: "Steak", would that also mean that Apple Inc., as company, likes steaks?
I'm not arguing, but merely asking and trying to find a logic of things.