You'd think that with technology and the acceleration of communication systems, getting a reply back would be easy. Not at all !!!!!
Probably it has to do with good manners, professionality and respect.
Have noticed that many TV shows invite viewers to post their questions by sending e-mails to them, stressing that you'd write with any questions regarding the topic they are dealing with.
Think of famous gourmet inviting you to write to them regarding your request to one of their recipes. What about sending e-mails to the contact you have reached on the web at the voice "contact us"? I get very upset when days go by without getting a reply back, especially from those who have invited me to write to them.
I find this very rude, un-professional.
Smart up, be wise and answer back to people that have contacted you.
It's only a matter of politeness and professionality.