That's true but that's not the reason. You need a box for each TV because that is what you will use to change the channels and the box need the RG6 cable connection.
I have read your tutorials on the HDMI cable and notice that there is "recommended" length to prevent drop-off. We have bought a new TV, a Bose bar speaker and are getting ready to hook it all up. When we talked to our DISH TV supplier, they said we needed to replace the in-the-wall wiring to any room where we put their HDMI box for a TV. We currently have RG6 in the walls going to 4 rooms and 4 DISH "regular" boxes. I understand the HDMI cable for watching a DVD from the BlueRay to the new TV/speaker bar, but do I really need to completely re-wire the house to get hi-def TV? Not everything is even broadcast in hi-def yet, so maybe it's not worth this trouble.