I would say cost...and looks. With the trussing at 30 degrees you probably should use strut and threaded rod to create a level surface from which to mount the plate that accepts the threaded pipe. Look into using the double mounts that allow you to mount 2 or 4 TV's from one pipe. Jobs like this take careful planning and wieght calculations to make sure you can support all the weight you are hanging above people. I have some pictures on my website of TV's we hung at Dave and Busters Denver, CO...under the project section
www.jbjsystems.com
Do you understand what I mean with the strut and rod?