This may sound weird and all, but ever since we started using organic, vegetarian fed cage free eggs our cakes have been turning out much much better. Moister as well as tastier. The eggs themselves seem to have more whites to them. When we cracked open a generic x-large white egg and a veggie cage free large brown egg open next to each other, it seemed you got more with the veggie cage free egg and in fact it made the brown cage free egg look jumbo sized next to the grade A x-large generic eggs.
Many of the recipes we use are from a Victorian cake book, so back then they probably got their eggs by walk out to the chicken coop. In contrast the box cake mixes are 'designed' around todays commercial eggs. I wonder if this is some of the difference we are experiencing here?