While preemies do encompas a number of children with disabilities, most of the kids diagnosed aren't micro preemies. Though I am sure the percentage of micro-preemies with problems is rather high in comparision to other children. The real interesting note is the genetic component in many of these conditions that is starting to come to life. I know they are starting to do studies that are tracing autistic tendancies in families of children that have been diagnosed with autism (I would probably meet the diagnosing criteria for aspegers even today and most defenitely would have as a child). As for many of the neurological disorders, I haven't seen much that points to them having a huge increase in diagnosis due to prematurity. I just don't think the data is there yet as they still don't know the cause or why some kids get it and some don't (versus things like CP, and even motor skill delays). ALso worth mentioning is that many LD's also tend to run in families (dsylexia etc..). The genetic trend is one reason wny i think the percentage of siblings that are also diagnosed are fairly high.
Another idea I have thought of is that many of these type of disorders kids end up with multiple diagnosis. Part of that may simply be that the main problem makes you less capable of coping with the world and thus you compensate incorrectly bringing about another condition (a lot of anxiety issues with kids with things like add, autism, etc..)
As for my family, I had the 2 pih/pe pregnancies and I had one aunt on bedrest for 7 months with PTL due to ovarian cysts. No other issues at all and we have at least 6-7 people who are already diagnosed or may meet the criteria for diagnosis of a neurological disorder. If you think about it, in older generations people were flighty, spacey, unorganized, wallflowers etc... today we see these same exact traits in terms of ADD, Autism etc..