Oh god I have been thinking about the same thing today!
Our DS1 was diagnosed with ASD 2 years ago and since then, some what we thought were good friends have notably disappeared. It makes me so sad the way people - adults and children - increasingly just ignore him, like he doesn't exist because he doesn't talk.
For example, we had house guests this weekend just gone, two kids aged 7 and 5 (same age as DS1). Used to be good friends, don't see them much these days. Their children totally ignored DS1 all weekend, obviously because he didn't know how to be entertaining and join in their games. Their parents hadn't had a chat with them about DS1 and that they should try to include him - be it looking at animal pictures with him if that's what he wants to do.
What a wonderful opportunity to teach your children that hey, everyone is different, everyone is good at different things, and just because someone doesn't play the way you like to play, he can still be your friend.
There was a point during the weekend when their eldest asked 'why doesn't DS1 talk' and the father pipped 'well, DD, he's just a bit slow' . To which I said, through gritted teeth, that 'actually he is very clever at certain things, he'll talk when he is ready but he is not ready yet'. This is a well educated, professional person, and that's the kind of belief that he is passing on to his children - that people with disabilities don't have to be bothered with as they are 'slow'. Nice.