Mike,
Here is an possible idea for your future distribution of Pleco for the iPhone/iTouch. If you have already considered it, please disregard this posting.
In the medical world, the heavy weight program, premium Epocrates Essentials was recently released for the iPhone/iTouch. They earlier released the free, basic Epocrates program for download through the App Store. To get this app onto your iPhone/iTouch device, you download a small free app from Apple that than requires you to obtain the complete app only via the programs free WiFi "Updates" function. As medical drug data needs to be frequently updated, the WiFi "Updates" function is extremely practical. What is neat, however, is that they seemed to have leveraged this feature in order to sell their premium "Epocrates Essentials" app through their own web site.
Basically, you have to go to their website (epocrates.com) and pay a subscription fee of $149/yr or $249/2 yrs. After you pay this, your account is credited and you will be able to get the full premium program through your next WiFi "Updates". I wonder if you might be able to use such a model so that you will have greater flexibility for controlling your sales and distribution of various dictionaries, updates, and for collecting more favorable payment through your own website rather than Apple's App store?
Epocrates is a truly high quality app from a top notch medical software company. I'm sure they've worked out this model with Apple, and unless they have some special arrangements, I wonder if you may find their model advantageous to Pleco's future on this platform.
Ed