This article is such crap, my son started school in nappies because he is severely autistic. He attends a school for children with additional needs where most children are in nappies but when we were applying I looked round mainstream schools as I had to present a balanced argument for his statement for why he needed not to be in one.
When I told them he would be starting in nappies the mainstream schools said they would accommodate as much as possible but would find it difficult as they had no place to change him and facilities for that. They didn't come across like this was something they dealt with regularly or dealt with ever really. They seemed to view it as a very unusual situation so I wouldn't say that they have a lot of children started reception class in nappies.
I think they only children who would be in nappies (rather than occasional accidents) and those with additional needs, needs which may have not been diagnosed yet or those with health problems which effect their ability to be continent. There isn't huge numbers of parents just not bothering to potty train their children, that is ridiculous.