what is the point of offering a digital copy if people can not put them on their ipods and have the only option of watching them on their computers.
You'll have to ask the studios that question, not Apple.
is there a way to be able to keep adding music to the ipod without having to sync stuff that was already on it?
Syncing only changes on the iPod what changed in your iTunes library. So after syncing it the first time, subsequent syncs are not loading everything again. It is only adding new songs and, if you removed songs from your library, removing songs. What has not changed does not get synced. Depending on your settings for things like TV Shows and Podcasts, after you watch a show or episode, that item may get removed from the iPod automatically. Also, data from the iPod, such as play-count, ratings, and On-The-Go Playlists, get synced from iPod to iTunes library.