Not true. I asked Shaw Direct this question awhile back as per this other thread, and they confirmed, they don't "charge again". You can watch as much as you want. It might be now with the new firmware that the recording won't work after 48 hours. I have 4-5 PPV movies on my PVR that I've watched well after 48 hours and had no issues.
Keep in mind, not everyone has their PVR hooked to a phone line, but rather call in orders (hence the new ID update), so without being hooked to a phone line how would shaw direct know how many times you've watched a ppv or if it was after 48 hours?