It also explains why you get poor percentages at close range; the target may be moving transversally, making it hard to swing the gun round fast enough while still maintaining accuracy.
You can't always explain it like that, and I'll tell you why. Overwatch.
Sometimes the game will decide to put an alien into overwatch, without moving it at all. You can, in your turn, move right next to him, and still have a good chance to miss (with a rifle at least, think you get better close range bonuses with shotgun).
I'll tell you what this makes me feel. It's less a combat sim, and more a "rock/paper/scissors" game. Rifles at close range are often non-lethal, and a shotgun at any more than a few squares distance will almost always miss.
So you can't have a squad, as you would in real life, all using assault rifles.
And in situations where getting close isn't an option, you'll never have enough firepower with rifles alone. So without grenades or heavies, a ranged firefight is a losing proposition.
That's part of what dismays me. In UFO you could play whatever way suited you and the situation best. You could have long range rifle exchanges. You could flank. You could creep forwards. You could blast the whole place with rockets and demo charges. You could launch a 14 rookie charge!
In XCom:EU, you have this rock/paper/scissors approach where the choice you have is really diminished. If you don't have the right classes on every mission - if you have 4 rookies, for instance - you're boned.
Playing in Iron man losing my squad does happen. And from the moment it happens, I'm boned, because I don't have the necessary classes to play rock/paper/scissors anymore.