Sorry but I am with Amo_Angelus on this one. It's not a perfect world and people do make mistakes, which will inevitably lead to the temporary escape of their pets (dogs and others).
In the first instance, the elderly lab had wandered off on his own, without his owner noticing and by your own admission, he was not interested in attacking or chasing your cat. In the second instance, yes, the owners let the spaniel off the lead but from what you say, they maintained control of what sounds like a well-trained dog and recalled him immediately and succesfully. In the final instance, you say that the owner has the dog on an extendable lead and the cat can immediately run to safety under the hedge - I would think that there is a good chance here that the owner doesn't realise that you are worried about the effect that his dog has on your cat, perhaps you could talk to him.
All in all, you really cannot expect the neighbourhood to alter their lives in order to suit you and your cat. It would be different, I think, if your cat was in any real danger but I don't get the sense that she is from your message. Sadly, it does seem as if the outside world is becoming less safe for pets - a cat in my area lost an eye at the weekend to yet another air rifle attack - and then there's roads. If you are really concerned about your cat's safety then I think that a "cat-proof" garden is maybe the way to go. Or perhaps even consider keeping her indoors (I have a very happy indoor pud).
Sorry I cannot agree with you on this one but ultimately, your cat's safety is your concern and none of the incidents you mention sound particularly worrying.
C.