1) The new system is completely different than the "Classic" MTS TV. Each TV needs a box because without it, you'll just see static/snow. The receivers are like computers, in a way, using a Microsoft program called Mediaroom. The old MTS TV system had three streams coming out of one receiver, so the 2nd and 3rd TV's were just being fed off the main receiver.
2) Yes, every home only ever gets one Motorola VIP1216 (the one with the hard drive in it), and up to five smaller boxes (VIP1200) which intercommunicate with the PVR, allowing your whole home to use the PVR function.
3) Pretty much answered in #2
4) You still need the receivers at every tv. If you don't have an HDTV, just don't subscribe to the HD channels. You can still watch HD channels on an old TV, and although the picture and sound are better, it still won't be true HD (TV must be capable of 720 or 1080 resolution for true HD).
IMO, I still think it's a great service even if you don't have any HDTV's. I really like the new menu style and instant channel changing. You may see a decent increase in your internet speeds by getting the new system, plus you can get free wireless at the time of installation.