Every skimmer, jetbike and jump infantry has the abillity to stop over impassable terrain, as long as the model can actually be placed on it. This limitation is reasonable imho, what would you do with a model that is in a place, it can't be placed.
It's like the rule, that models can't move through spaces, that are smaller than their bases. Obviously, they could worm their way through much smaller openings, but it is just not usefull in a game, to asume what could be, but can't be done.
By the way, no skimmer lands between it's moves, this assumption originates from the 'moving skimmers' paragraph on page 71 in the BRB, that says, that skimmers must be set down at the end of their move and can't be left hovering in mid-air.
This follows the same mindset, in theory a skimmer could alter it's height while moving, could fly high to shoot over a building or low to hide behind a small wall, but to make the game simpler it is impossible to do this in the game. And afaik this will not change, neither in the next edition, nor in any future ones, as long as it is not playable.
I must rule with eye and claw — as the hawk among lesser birds.