Based on what you want, a "web app" (really just an iDevice optimized website) sounds like the best solution. Assuming the wordpress can spit out some type of formatted data (RSS, XML, JSON, something like that; or if you can use some server side scripting to access the data), building an optimized site would be pretty painless.
I haven't worked with wordpress to know what it's capable of, I kind of assumed it was a web based iWeb.