This is because many cable boxes do not have HDCP repeaters implemented.
Silly. But, the only thing you miss out on is convenience. nothing else.
And besides, by having a direct connection, you benefit from getting to calibrate video per source input.
I originally set out to find the answer to this problem but i was able to locate the answer somewhere else. But for those having the the issue where the box, after being on the same channel for a couple hours, completely locks up. Remote doesn't work and the buttons on the face of the box do not work either. And the only way to unfreeze is by unplugging the box. So, i went thru 4 boxes from comcast and had a tech out to my house for a few hrs trying to solve the issue. They couldn't figure it out at all. The problem has to do with there HDMI connection when being passed thru a receiver. Once I changed my thru-put to the component cables the issues stopped. Apparently the Motorola boxes see the receiver as an unidentified device when connected via HDMI and the boxes can't handle it for some odd reason. My other HD DVR is connected to my plasma via HDMI but is directly connected to the TV and that has never frozen. so for anyone having this problem try the component cables for pass thru or direct connect HDMI to your TV and see if that helps b/c apparently comcast doesn't know its own equipment and will have you swapping boxes til you die. Hope this helps someone.