Presumably because the soil is more moist? In which case, why are you applying water?
Because in the drought scenario, the soil is absolutely dry. Some of the water will be wicked away by the utterly dry soil. We're talking about cracked desert soil, not anything you'd expect to grow anything, including cactus.
So in more normal scenario you still need to water the plant. But the surrounding dirt still has a little moisture, and so it doesn't wick away as much water.
Think utterly dry sponge vs. very slightly damp sponge.
Water travels through soil only due to gravity, and that is downward
Nope. Capillary action still works. If you water only the center of a houseplant, you'll find the edges of soil are damp after a little bit.
Besides, the plant will send its roots in pursuit of water. Why else do you think your stupid pine tree has roots tearing up your sewers? So even if the water did not "remain near the plant" (which it actually will), the plant will send roots out to get it.
This isn't a scenario where the water completely disappears. It's a scenario where you need to add additional water to overcome what is lost by water being drawn away by the "utterly dry sponge" soil. You just need to add a little more to get the same concentration of water at the plant.
Not really. Clay pots will allow the water to leak out, so they should be provided with a waterproof lining, but otherwise once the surface of the soil has dried out no more evaporation can occur because the water cannot move upwards to do any evaporation. Gravity rules.
First, "water cannot move upwards" is false. Capillary action still works. That's why you don't end up with super-wet soil at the bottom of the plant, and utterly dry soil starting half-way up.
Second, pots have bottoms. Even if you were correct about gravity being the only thing that has an effect, water can still leave the container.
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