Josh may have been on probation or parole and wasn't allowed to leave the state/county. That may be why he wasn't along on vacation with them.
That would make sense, and I don't remember exactly what happened, but I do remember it seems as thought she was just mad at him, and told him that she couldn't trust him and that was why he couldn't go. I can state with certainty that the reason Laurie gave on the show(and who knows, it could have been edited for effect) was not anything to do with probabtion and him not being able to go anywhere, you could tell he was really heartbroken about it. And I am not excusing Josh's action in any way, I just think that some of his problems may be a result of Laurie's parenting. I have hear some terrible things about her, but they could be untrue also. I just really don't like her, she seems in it for what she can et out of it.