One problem with the Turing test is that it turns out that you can do pretty well by just using some very simple tricks and techniques to appear as if you're understanding the conversation - picking a noun from a sentence and asking a question about it, for example, or starting sentences with "yes, but" and going on to say whatever you were going to say anyway (Turing obviously didn't study the interview techniques of politicians). A few of these heuristic tricks put together can go a long way towards convincing a naive interlocutor that the machine is a person. The problem is that to get beyond the 90% horizon and convince somebody who knows what to look for, you need vast complexity. In most fields of AI it's a similar situation - simple heuristic tricks and techniques give you 90%, but any advance on that requires mind-boggling complexity.
For example, a simple way to identify a machine interlocutor in the Turing test is to make obvious references to historical context, the sort of stuff that any human might be expected to know about, but a machine won't unless it's been explicitly told - the second world war, the world cup final, that sort of thing.