Can't speak for i-movie, but final cut does not reencode on capture (although you may be able to set it to do so). You set the format that the tape is, and it captures in that format. As far as exporting, if you export as quicktime movie, and DO NOT check recompress all frames, and keep the drop downs as keep current settings, it will be a lossless copy that can then be imported into Final Cut. Quicktime is just a shell, it will maintain whatever codec it was created with (HDV).
Perhaps you were confused because in actuality, your camera records in a compressed format, an HDV variant of MPEG2 (it has more keyframes than your average mpeg2, making it easier for your computer to edit). Uncompressed HD is the realm of pro equipment only and is very expensive. HDV does a fine job though. I've been using some FX1's for a couple years now. Although it is a compressed format, FCP will allow you to edit in that native format, without any loss. You must set your capture settings, and then during editing set your sequence settings to match.
Sorry, can't speak on imovie, but I'd imagine it has a bunch of annoying things that would make you want to upgrade to FCP.