Parents and In-Laws

So I wanted to celebrate Nathan's birthday this week with my parents an in-laws for a dinner together. When I tried to schedule something, my parents absolutely refused to have any association with my in-laws. The last time they saw each other was at the hospital when Nathan was born. See, before the whole falling out with my parents when Nathan was born, my parents already hated Dan's parents. Even before we got married, they weren't acceptable in their eyes. They think that Dan's parents are rude, loud, obnoxious and aggressive. After getting to know them during the whole time we weren't talking to my parents during Nathan's first year and a half, my opinion of them has completely changed. Yeah, some people may think my father in law is a bit loud or whatever, but they were very supportive and loving towards us. They're the complete opposite of my parents - non-judgmental, non-criticizing, very loving, forgiving, etc. In fact, if and when the time comes to take care of our parents, I'd rather live with my in-laws than my own parents (really sad to say that). I was really saddened that my parents couldn't "tolerate" one evening with them, even with Nathan around to "lighten" the mood. In the past before Nathan was born, we always got together for Thanksgiving and Christmas, but now my parents want to do everything separate from my in-laws. I'm thinking it's a combination of a lot of things: they were embarrassed by the whole situation when Nathan was born, they don't like my in-laws, etc. I guess I'm being a bit of an idealist and am asking too much for my parents and in-laws to get along since this is probably not the "norm". Does anybody else's parents and in-laws get along or is this normal to do everything separate?