I have my TV wall mounted on a thin wall (1/2" drywall, 2" deep metal studs) in my condo. Because it was thin and the wall is used to run cable, power, and telephone lines to the condos above I used plywood on outside of the wall to reinforce the brace. With 8 toggle bolts the thing is rock solid.
I want to hang a floating shelf above the TV now to hold the cable box and dvd player. Would you expect there to be any issues hanging the shelf into the studs above the tv? Just looking at a simple lightweight one from IKEA and the electronics probably don't weight any more than 5 lbs.