Well I had a download going, went to play Crysis 1. Played for 8 hours. Download did not increase by even 1KB. The download was just "pending". If it truly was downloading at SOME rate, it'd say so
Yep. Crysis is one of the more graphic intense games on the PS3, so it probably does cause the download to pause. Uncharted, God of War, Demon's Souls, etc probably also pause downloads due to their graphically intense nature. Doesn't mean there is a function in the software that actively pauses the download, the game just uses 100% of the PS3's resource. Even if the download is continuing at a trickle while you are playing, just bringing up the XMB to check on it probably pauses the download.
I would assume this will be addressed in the PS4 with 8GB of RAM, and that the PS4 will allow for full download speeds when you are playing offline.