Matapatos,
You had asked my that question about broodingin the PM .
Finally got a second though I would answer it a little here.
As for natural over boxed brooding Obviously the hens do all the work in the natural form. The risk with that invovle uncontroled wondering of the babies, possible escape from the pen and some thing getting them, drakes killing them etc.also the hens are done laying for the season at that point where they would possibly lay again if you did it.
The pluses of it, the ducklings parent raised, barring any of the above problems, often do much better, arent in a messy brooder (that you have to keep clean) You dont have to constantly watch the lights (and pay the power bill for them) and you dont have to worry about them being water logged when first introduced to water.
Boxed brooding has 2 forms wet and dry. Dry is what most people use and is the same as any chicken brooder. Here they are safe from being killed or getting lost and are in a more controled enviroment. You do have to be dilgent on cleaning it to prevent bacterial growth that may rarely cause problems, but you need to that anyway.
Wet brooding is the same, but they are given water to swim in which helps with feather condidtioning, and is pretty much manditory with some diver species like the stiftails.
Commercial set ups are the same, just larger more expensive set ups,
As for the question of abbandoment , large broods, and small broods.
Any of them can abandon a nest, not too many will abandon a brood though.
Treeducks were always the worst for me on "nesting" anyway, most just did the drop it and forget it aproach. Wood ducks, mandarins, ring teal, were all great broody moms.
They treeducks will lay probably the most eggs per clutch, 15 is'nt uncommon for them and they are the most protective mothers if they do decide to raise them, hottentot teal ruddy ducks, any of the small guys really, 2-4 is a good number for them.
Most of the normal sized puddle duck species will do 6-12 on average, most divers 2-7 on average.
Hope that helps a little on that.