I feel that in this discussion there has been a bit of a misunderstanding or confusion or unintended emphasis given to comments made by some of us, myself included, about Kate and/or William knowing better. It's not blaming Kate, i.e. saying it was her fault rather than the perpetrator's. It is merely saying that in much the same way as people who choose to swim in the surf on Western Australian or South African beaches at dusk run a very real risk of being attacked by a great white shark, there was a very real risk. Like the surfer, Kate and William should have been aware of the risk of a hidden predator attacking and they assumed the risks inherent in the activity.
When there is as much interest in you as there is in Kate, unless you are 100% sure that there is no way someone could photograph you with a modern telephoto lens, i.e. unless your security people know the location well and have made lengthy and thorough checks to ensure there is nowhere from which a photographer with the right equipment could snap a pic - and, IMO, in view of the prominent location of that residence in hilly country, there should have been real doubt about that - you don't do something that you wouldn't mind seeing immortalised in a photo on the front page of the paper.
It was most certainly an invasion of their privacy, but they should expect their privacy to be invaded, because, like it or not, that's an incident of their lives, which, again like it or not, are lived in the public these days. The line between public and private is a fine one due to modern technology and instantaneous communications. And William, who has been royal all his life, and the son of Diana, should, of all people, be only too well aware of these facts. He might not like it, and I'm sure he'll huff and puff about it and denounce the paparazzi and issue lots of lawsuits, but, like shark teeth, new paps will keep popping up the moment one is knocked out. It will never end for them. I hope he accepts this and accepts the need to behave very cautiously in future and doesn't make it a mission to tantalise the paps and then chase them in Court. That could get tiresome.