QUOTE
as a weight savings move, nothing more
Three reasons... none of which is really weight.
1. Heat. When the brake pad grabs the rotor, it creates friction, which creates heat. If that heat can't escape, it leads to brake fade, which reduces the brakes' stopping power. How well that works on a solid rotor without venting and cooling vanes? I doubt if it hurts.
2. Gas. This actually isn't much of a problem any more; however, materials used in some older pads caused gas to build up between the rotors and pads limiting stopping power. That was the main reason cited for drilling rotors on sports purpose vehicles.
3. Water. If a car drives through a puddle, or a rainstorm, the brake rotors can get wet. A wet brake rotor can be slippery for the pads to grab. Having drilled holes makes it easy for heat, gas and water to be quickly moved away from the rotor surface. Not sure I've ever noticed this (the water thing) on a non-drilled rotor but, that's what they say.
The obvious downside of using drilled rotors (as mentioned many times) is that all of those holes tend to weaken the rotors. After repeated stressful driving, the rotors can crack. Some don't as you can see here... rear brakes don't get as much of a workout as the fronts probably saving them from the stress crack scenario.
Chris, have you set your venting clearance lately? Those rotors don't look like they're getting "blued" which, with your driving style described, they should be.