Ask HN:When to expect reply to emails?
growt: If you comment on a product or website that is "hot" at that time, the authors may be overwhelmed by the feedback they get and keeping the servers stable at the same time.
Happened to me once with goosh.org, I got approx. 500 emails in a few days after the launch. I tried to answer them all anyway.
But I think big corporations that have the money and manpower should answer every single email (yes google I'm looking at you!)