This is not the case. The only circumstance where this is true is if you downloaded the DIVX patch on one console with your profile and later on re-downloaded it on a different console using the same profile (it actually says already downloaded where you select download again). And even in that case, you can login to live, play a file, exit out of that file and log out of LIVE. You will still be able to play the file even when you are now logged out, but you do need to have logged into LIVE once if you have turned the console off. You need to do this everytime you have shutdown and restarted your console. But on the original console I downloaded the patch from the very first time, that console does not need to be logged into LIVE.you need to be connected to LIVE in order to play DIVX (no clue why).
It's a hassle to do things on your standard PC. You have to hook it up to your HT Receiver (which may already be short on inputs), then you always have to get up, go to the PC and open menus, windows, navigate to directories, open up the file with the viewer, maximize it and play. You have to get up every 20 minutes if you watching half hour tv shows and do most of that again (if you don't have wireless keyboards and mice - which you'd have to go out and buy). It is general more cumbersome.If you have your PC close enough to connect it to your xbox 360, why not just connect it to your TV and play the video in a divx player from your desktop? Why would I want my xbox running?