My son has sensory integration disorder and was diagnosed at 4. He has social skills problems which are very common with sensory kids. Add speech issues to that and yes, peer interaction would be difficult. We worked on many social skills concepts quite diligently and while we still have some issues with my boy trying to "control" the situation to his liking, he is doing fine. He is 6 and in kindergarten and has no issues in the group setting. Your early intervention can make the world of difference. Good job mom!
If you think there is a possibility of your son having Autism, the first thing to do is to quit wondering, and see a specialist to find out. Then depending on the specifics of your sons diagnosis, if he does have it, set up a routine, and post it around the house using pictures and words. There are a lot of therapies for children with Autism, and decisions will have to be made (such as if and when to utilize medication). Most importantly though, there is no cure for Autism, and the sooner you accept your son for who he is and realize that you did not do anything to cause this, the sooner your family can start moving forward. Please understand, I am not trying to be mean or harsh. I went through these very same feelings during the process of my son being diagnosed with Autism. He has a mild form, and is considered high functioning, and he is a sweet delight of a child. He just sees the world through a different view, and that's ok. Have faith, trust your instincts, and all will work out.
He sounds like a pretty smart 2 1/2 year old actually. All children develop at different stages. I work in a preschool and there are 4 year olds that still aren't at the level that your son is so I wouldn't worry too much.
It's great that you have him integrated with other children...that really helps with social skills.
As far as children being "therapied" into normalcy.....I think it all depends on the child and how early things are being approached.