>> Yeahhhh.... that isn't always the case, especially not with trees. At least, here that is.<<

America is bigger, so fewer places have restrictions on what can be planted.

>>Ditto with water courses and so on, what you do affects whoever's downstream.<<

Water people will fight over, but that's natural water. Boss Blaster didn't do anything new with water, just managed what was already there.

>>That said... the old homeowner could've sued them because of the run-off affecting her property. <<

In theory, yes. In practice, people who can afford to lay a parking lot have more money and clout than a little old lady.

>> and the new trees should bind the soil nicely, as well as control the amount of subsoil water due to transpiration.<<

Exactly. The new plantings will keep the water from becoming a nuisance and help sop it up.