Yes. The iPad 3 was significantly thicker and heavier than the iPad 2. It takes a larger battery to drive 4 times the pixels and maintain a 10 hour battery life.
It is 0.6mm thicker and 50g heavier. That's a 6% and 7% increase, respectively. I wouldn't really call it 'significant'.
The retina display is significantly less translucent, requiring a greater backlight for the same brightness on the front of the panel than a non-retina.
The backlight being the lion's share of the battery consumption, this requires a significantly larger battery.
do the pixels weigh more? Seriously, would faster graphics weigh more? Or are you saying juicing the graphics would eat more battery, and therefore, it would weight more?