Having supported Eudora on both Windows and OS X, I'm inclined to take any attempts to shift the blame to other parties with extreme skepticism. The impression I have is of an old, ugly codebase which dates back to the 16-bit dark ages and isn't abstracted much at all, leaving legacy hacks and deprecated API calls all over the place. Modern features like IMAP really feel like they were crudely hacked into a model which wasn't designed to handle them.

This really sounds like sour grapes from a developer who for one reason or another doesn't like OS X and is looking for points in favor of his position.

Gen: you can import Eudora's mailboxes directly as they're just the usual Unix mbox format. Alternately, if you have access to an IMAP server you can sidestep the issue by storing your mail there - I recommend this approach as it allows you to use both clients simultaneously instead of having to commit to one.