Steve, it sounds like www.purplebananas.com is the same as the keyword you're needing to rank for, correct? A couple possibilities here:
1. SEOmoz's data is inaccurate.
2. There is a quality issue with your site on some level.
There has been some significant Google algorithm updates for exact match domains recently. It may require an inclusion request to Google after you've made some updates. If you haven't already, make sure you're using the latest version of Wordpress and install Yoast's SEO for Wordpress plugin. Make sure your XML sitemaps and Robots.txt are set up correctly. Also, make sure you're in compliance from the Google Webmasters Tools perspective (no notices or warnings).
If you find that you're not listed anymore for your domain name, it's possible you've been removed due to a trademark penalty, which means there's some significant issues with duplicate content or Google thinks you're trying to spam it in one way or another.
Having a pro evaluate the site and your various TLDs for major no-no's may be a good solution if you cannot resolve it with the steps above.
Hope that helps and best of luck.