Mini - sorry that sounded a bit defensive on my part. Didn't mean to! 
I think it's a bit of both - some children are being failed and some parents are very pushy.
As a forum about primary education, MN obviously attracts people who are interested in their children's education (sometimes, it would seem, too interested
).
As parents are 'letting their children go' for the first time, parents of young children have demands that the school needs to address - social, emotional and academic. This is a huge area of responsibility for the school, and we can't hope to please everyone. This is where MN comes in useful, so people can vent spleen about what they're unhappy about. If you analysed all the posts, I think the subject matter would be very narrow (e.g. reading books (levels and how often books are changed); private/state debate; toiletting; KS1 SATs; phonics; writing; giftedness). I guess it's just an improvement on the school-gate - where you can ask sensible questions without any gossip or bias, and get useful answers.
I also think that many parents of young children expect their children to progress linearly - you know - 'learnt that last week, learn the next thing this week', and they feel that they're not making sufficient progress (and many blame it on the teacher). They don't understand that children need teaching the same thing over and over again. They can only take in a certain amount at a time, as they haven't yet built a big enough scaffold to hang their learning on. Doing things again and again reinforces learning and prepares them for the next step. I think, when parents criticise teaching, their child sometimes hasn't been ready to take that next step.
Because of the narrow demographic, I don't think MN represents views of all users of the state school system, and I certainly don't think that the system is falling in ruins around us. I think it's too rigorously controlled for that.
On the other hand - I find some of the comments about what is happening in some schools totally shocking and wonder how they get through their Ofsteds!