What we try really hard to do is not penalise the player for things beyond his control - this means that we do let a lot of stuff go.
Crossing requires 2 players. As you will always be controlling the ball carrier, it means you will have run into a player controlled by the AI. If he's in a dumb position or running lines that you feel he shouldn't, it would be really annoying. So we do not call it.
Offisides do get called sometimes, but we let it go a lot - particularly if the offending player is off-screen. I know this isn't accurate as a sim, but it makes the game flow better.
Stuff around the ruck - killing the ball, hands etc. is really difficult to implement without changing the focus of the game. And I apologise to the hardcore rugby enthusiasts who subsequently think our game was too simplistic. What it does do though is allow the game to be played by novices and people who do not necessairly understand the rules. That's got to be good for our sport.