I'd say one thing - Techcrunch is definitely NOT the only game in town for PR. They are very fickle and clique-y. There are huge startups that never made a dent in TC. PR is all about building buzz from the ground up, exclusives are a load of crap and mostly reserved for established players anyhow.
If you're not getting any coverage from anywhere, yes maybe there's something at the core that isn't compelling (and you need to talk to customers / users first to determine that), but chances are you aren't spending enough time sending fun personal emails to lower-level bloggers and journalists. If you aren't in the elite old-boys club, you shouldn't be focused on approaching the journalists who are.
But PR and "viral" launches are hard work. The idea of the massively hockey-stick organic viral launch is largely a myth propagated by a few outliers (aka survivor bias).
And good PR does not make a success, either. I've built 2 things that made big PR splashes (everything BUT TC haha) and neither landed me either fame or fortune. The one product was blogged about by the New York freakin Times, and it never achieved escape velocity. PR isn't a long-term marketing strategy. Its a one-time high and believe me the downslope doesn't feel good either
Honestly, there are 2 types of folks who make it: the lucky ones, and the persistent ones. Its hard as hell (and heck I haven't beaten it yet) but you have to ignore the burnout and be one of the persistent ones