It may be worth moving in a slightly different direction to traditional PR services. I had a similar idea a few months ago - offer up the press releases in a variety of formats for webmasters to consume.
There are hundreds of news blogs and news aggregators that are hungry for decent content for their sites. Give them RSS feeds that they can manipulate (filtering by category or keywords for example), or widgets that format the feeds in nice boxes or tickers.
Perhaps also newsletters of the latest releases in certain categories or keywords, or even an "industry watch" style search that will group releases of a similar nature into a threaded style.
It's all about how you publicise the content. Go for something unique that encourages wide re-use of the press releases. Not only will it get the word out about your site, but it will impress potential submitters with the possibilities of thousands of people reading their release
