Okay - I want to really make sure I understand too.
So - movies and books seem to be a pain in the neck right now if you want to watch/read while you're on a plane or on a beach. It seems that every app out there wants us to have an internet connection to watch/read.
Is iTunes/iBooks the only app that will truly allow you to download new, puchased and legal content or video to your iPad and watch/read without a wi-fi or 3G connection?
You don't need a connection to read a book once you've downloaded it. Downloading often takes less than a minute. That's unless you're somehow reading a book online, which is relatively rare. (Some textbooks and professional training books require this, for instance.)
You can legally load movies onto your iPad to watch later without a connection, without buying from iTunes, but the conversion takes time. For instance, you can buy a DVD, convert with HandBrake, add it to your iTunes account and load it on your iPad. This type of use would be legal if you'd purchased the DVD and used the copy for your own use (instead of distributing it for free or for money, because you're buying rights to use, not to distribute).
I frequently read books and watch movies on iPad without a connection (on flights and elsewhere where I've turned off my connection). Transferring movies is a pain simply because of conversion time, though.
Buying movies through iTunes would be a quick alternative, but I prefer to buy my movies in DVD form, then convert. If you buy through iTunes, you'll probably want to back up your movies, because Apple assumes that responsibility is yours if something goes wrong (say if you accidentally delete the movie, you'd have to buy it again).