The MPEG standards are compression not encryption. As far as the letters, if a subscriber (me) still had the older Rovi cable-boxes (MPEG-2), Cox instructed me to swap it for Contour (MPEG-4). I can't remember if the letter addressed cable-cards...probably...but it clearly read if I delayed, I'd lose some programming. MPEG-4 compression uses lower bandwidth.
This "rollout" was at least 3 years ago and I'd be surprise if any channels were still MPEG-2. I don't know much about TiVo but if you're getting all your channels, your card probably supports MPEG-4. For example, HBO probably has 9 channels but my Rovi could only tune 3. When I got Contour, I could tune all 9 channels.