From the Flight Attendant Manual, Aircraft General Policy, Powerports and USB ports:
"Only one device is allowed per outlet, splitter (or Y) power adapter cords may not be used."
Here's an interesting one I did not know...
"Powerports and USB ports may not be used to recharge batteries; however, electronic devices containing batteries may be plugged in, as long as the device is switched on."
Since the why on both of these quotes is not included for f/a benefit, If you know better than the policy makers I'm afraid you'll need to discuss it with an AA employee well above my pay grade.
As far as never being challenged for using a power strip, fortunately I am not responsible for other flight attendants not doing their jobs. When deadheading or nov-revving I also see flight attendants allowing bags, etc on the floor on bulkhead rows, but that doesn't mean it is legal or allowed.