Not sure where I am with this at the moment. B and Sil, who incidentally (or not, can't decide) live in quite a tough inner city area, refused to accept their ds's issues were ASD and as a result school etc took over. Dn had full time 1:1, scribe and just about every other intervention possible, without a statement and has had an excellent outcome. This came about because the school has lots of experience of dealing with children with various additional and/or special needs and therefore has the experience and facilities to just get on and help those that need it.
My two nieces, also living in tough areas and with difficult homelives, both have young ds's with different SNs. Both have speech/language problems, one in all likelihood has ASD and ADHD and the other probably ASD, but could be more complicated. Both have been identified young, had portage and playworkers, SALT and are on the path to more intervention, dx and probably statements. Neither dniece has had to push or fight for this.
Ds on the other hand lives in a lovely, leafy well-to-do area and attends a 'supposedly' excellent school, that refused to either recognise or support his issues so we had to bypass them and bring in assessment and support ourselves. Years down the line school is on it's 4th (and seemingly best qualified) SENCO but is only interested in paying lipservice to inclusion and making things look right on paper (tick-boxing).
Ds is a mess, anxiety through the roof and no-one will help. GP said go via Paed, because he needs CAMHS and they will listen to Paed, Paed said CAMHS won't see him because the anxiety is school related and it's therefore down to EP, EP said ds is lucky to have/have had the support he's had thus far (so that will be a few sessions in 2010 then, which encompassed part of his ASD assessment) and all they will do is teach dh and I some relaxation and mindfulness techniques, as 'he has to learn to handle the anxiety himself, because, having ASD, it's not going to go away'. 
We have been as good as told that because we are intelligent, interested and capable parents who will fight for and help our ds in every way we can, it's down to us to help him. We are essentially on our own.
BUT then again, although we hear the same stories over and over, I don't think it's a simple and clear cut as the scenarios I've just recounted would seem to suggest. Not all the vulnerable children in tough areas get noticed and supported, not all get overlooked and let down - same goes for children in naice middle-class schools. To some extent it's the luck of the draw, which LEA you are in and also very much down to the individual professionals whose path you happen to cross.