T
thesloppy
Watering from the top will push the freed up nutrients down to the roots. Bottom watering will pull them away. You soak your soil, then it drains to waste.
As Verd put it, it's a more direct air exchange. Water pushes down the air which gets trapped or travels back up through the medium. More action.
While nature depends on ground water. dew is present which keeps the top moist. When the rains come everything flourishes and reaches it's prime.
I feel I should note something: Straight bottom-watering is not an optimum way to feed your plants. Once the discussion gets rolling, and people start talking about their favorite techniques, it can sound like people talking about bottom-feeding are promoting it as a more efficient/productive way to feed, which it most definitely is not....realistically, it offers nothing more than a way to water/feed your plants less (which is probably a bigger concern in coco, than soil), and make the process of watering easier. It will effect your yield negatively (though not drastically, in my opinion or experience), and anyone considering bottom-fielding should definitely take that into account.
I've spent many days plumbing the depths of the PPK thread Snook mentioned, and there is a ton of good information in there, at a depth well-beyond any other thread, and if you're looking to know the science (both 'real' and anecdotal) behind top/bottom feeding, and get actually increased yields from a 'lazy' watering system, that's the place to start and finish.