I have lived in China for the past 5 years, and have a lot of friends who were previously using Palms/Treos - mainly because of PlecoDict. They were either English speakers who needed a good Chinese dictionary, or vice versa. Most of them have now switched over to the iPhone over the past year, and one of the things that they (and I, obviously), really wish we had on it was PlecoDict. Some have been able to use WeDict - but it is completely unsatisfactory.
Most of the folks with iPhones in China use US credit cards to buy applications from the US App Store. This has also been the case for those based in Singapore/Malaysia/Hong Kong, and many other countries in the region. With the "official" launch of the iPhone in Asia over the past month, the market for PlecoDict on the iPhone is even greater now.
To echo the sentiments of the folks above, I think most of the folks I know, who have depended on PlecoDict for business discussions etc in the past, wouldn't mind paying a tad more to cover the App Store cost, if need be (but, similar to the chap above, I do think the addressable market would be much bigger now).
Also, it should be noted that many companies are "beta-testing" their iPhone apps during their development period, with an intention to charge once their products are complete. One company that is doing this well is Omni (with Omnifocus). They post updates to their iPhone application on the AppStore on a daily basis, and building a great relationship with their current and future customers this way.
While Copy/Paste would certainly be useful in the future, for transferring data between apps/from SMSs etc - it is only a small part of what makes PlecoDict so useful. I do hope that Mike will consider developing it for the iPhone platform soon.
TT