While I agree with the sentiment, and absolutely agree you should never engage with a service animal without asking the human first - and being fully aware that they are busy people, and have no desire (I would assume) to deal with busy-body strangers... referring to a service animal as "just like a pair of crutches or a wheel chair"... like an inanimate object, just doesn't sit right with me. Service animals are so much more than a tool... as the one in the first link proved - the dog noticed the out of control car first. An oxygen tank couldn't do that. A service dog can perceive a threat and push their human out of the way. A wheel chair can't do that.
I admire service animals, and no matter how much I want to go hug them and let them know, I respect the privacy of the working pair and try to go about my business without interfering in theirs.