Essentially yes, the Directv Cinema are mostly 48 hour rentals (some more, some less, but all are rental). After purchase and the time running out if you try to watch again off the DVR you'll have to pay again.
Tell the greedy studios about it. It isn't Directvs choice. Even the free on demand things have expiration dates. I download music videos on the MTV and VH1 on demand channels and they are automatically deleted when they expire.