This association with specific groups seems to hold true in the world of disability, too. Depending on our diagnosis and current status, we usually associate with others having similar problems. I'm sure this has much to do with the fact that we are more comfortable with others who have similar issues because they understand what we might be experiencing or going through. We gain comfort and support in this way.
This disability culture frequently has it's own discrimination problems, too. How could that person with a head injury possibly understand what it's like for us with spinal cord injuries? Kind of the 'Rudolph the Red Nosed Reindeer' thing; he can't join us in our reindeer games, he has a red nose.
As with all groups and people, we should try to be supportive to all as best we can. I pray that we focus more on what we have in common and less on our differences...