Actually the rules are designed to encourage large armies that sit on either side of the board and shoot at each other, i.e. a higher model count.
There are no risks because there are not people doing it. Since the dawn of 6th Edition (and continuing until now) I've seen only ONE plane successfully deliver a cargo of assault troops.
This is because it doesn't work and most people don't try.
There is nothing wrong with it, no. People just don't use them as they are billed. There is a lot of humor in it though, i.e. that assault vehicles are never used as such because of they are utter garbage at doing it.
Again, no they don't work. They will never work. You appear to have missed the brutal timing and math aspect. If you use them to deliver your expensive, quality assault troops you are ensuring that a significant portion of your army will NOT get into combat sooner than the 3rd or 4th Turn (when the game is already half or more than half over).
If you are invested in winning the game via assault, this is tantamount to setting a bomb with only a thirty second timer and you have ten stories of stairs to go down before you can get out of the blast radius.