One of my friends, let's call him Tom, is in a fairly successful band (especially in his local city). Tom couldn't get the radio DJ of the local show to reply to his emails or play his band on the radio show and Tom felt he deserved to get played. After about 5 emails, instead of calling the DJ or getting a mutual friend to put in a good word, Tom wrote a scathing email to this DJ using phrases like "I hear you're a good guy, so what gives?!" Big no no. Guess what came of this? Tom's band never got played - and probably never will.
The worst thing you can possibly do (and most tempting thing to do) is to bitch someone out via email because they never got back to you.
The biggest reason why someone doesn't get back to you is not because they hate you, it is because they don't know who you are and don't have time to get to know you right now. That being said, most likely they're not assholes, do like getting into new music, and will get back to you if you're persistent.
The key to this industry is "polite persistence." I've gotten nearly everyone to reply to my email through this method (even rock stars and big time managers). If after 3 beautifully crafted emails they still haven't gotten back to you don't get discouraged. They'll scan your email each time - if not just the subject line or sender field - and each time they'll make a mental note. If they see a 7th email from you with each one more polite than the last, they'll eventually write you back.
I know it's tough to say the same thing over and over again, but find a way to be just as kind each time with different wording.
The old booker at the Varsity Theater in Minneapolis once told me that he felt so bad that a band had politely hit him up 8 different times and he never got back to them that he eventually just gave them their own show - no questions asked. They weren't a buzz band and they didn't really have a draw. Sometimes all it takes is being a nice guy and being persistent.