I agree about balance. I have certain rules in my home about what we eat and what we can see on tv and so on, and rules about what kinds of clothing and toys and products I prefer to spend my money on, but I don't like to take it to the extreme. And at other people's homes, unless something is really against my beliefs, I don't make a huge deal. If there are cheese doodles for a snack, dd can have some, as long as she doesn't gorge on them. If the mom serves the kids lunch in front of the tv, I may cringe internally but I say nothing. IT'S NOT GOING TO KILL HER. Besides, she's learning about how to be a gracious guest. And she's learning that there are different rules in different homes. And she must be learning well, because usually she will ask me permission when she is offered something in someone else's home that she is usually not allowed in our own home. I think she appreciates that I usually say yes, too.
As far as not being able to join in on games, I like the idea of teaching a child to say, "No, I don't watch that, but if you teach me how to play your game I'm sure I can keep up," as pmjmomma suggested. I agree that they should not learn at such an early age that the only way to get along in a group is to do the same things as everyone else. Dangerous lesson, if you think about it.