Why does it seem like exclusively fed infants weigh so little?

I exclusively fed my son - he was a big baby and stayed big - he's always been at the top of the chart for weight and length. You can't overfeed with feeding, but you can with formula feeding. A lot of the variance in baby weight and growth is purely genetic. I've seen people abandon feeding for formula feeding because they felt their baby didn't weigh enough - and it made no difference.