This has happened to me probably more than I can count. The worst was when a potential employer/manager led me on, and even seemingly *begged* for me to join his team, stating that a lot of my friends were there (I used to work for the company prior to when they were bought out by a bigger corp, so I knew a lot of people there). I had multiple phone interviews with the guy and even went in for an in-person interview, but then he just dropped all communication thereafter with no follow-up. I had to find out they went with someone else from one of my friends who works there - I was so pissed about that.
Ironically, I ended up getting hired on to work there under my old boss/friend and had many interactions with the lousy manager and his team. I soon found out how terrible of a manager he was/is - he was let go even before massive layoffs occurred at that place too. It was sort of a relief once he was out because he was the type who liked to blow a lot of steam and not actually have anything to show for it (and this is what led to him getting let go, I'm sure). Even when we were having discussions in the same room, he always tried to make things difficult and either I or others would get into quibbles with the guy... he was just difficult to work with.
In retrospect, I'm glad things didn't work where I would have been hired onto his team - I'm pretty sure I would be miserable if I were working for him. In any case, if they aren't cordial enough to get back to you, it goes to show they probably aren't someone you would have wanted to work with. Sure, some places may be busy but in my experience even if you initiate the follow-up, they will usually make time to get back to you - and if they do, that just shows they are a place that you would enjoy working at.