Meh, I absolutely 100% agree that that all dogs should be held to the same standard.
When it comes down to it, whether I'm getting treatment for the bite of a chihuahua or treatment for the bite of a lab, I'm still having to get treatment from an attack simply because I walked down the street. (Using the OP example)
When you start to exempt breeds that are under a certain weight, you're just setting up BSL.
Plus, like somebody else said, where do you draw the line? What's the weight limit? An attack from a 50lb dog is going to be much worse for a child than it is for me, and worse for me than it's going to be for, for example, my father.
Another analogy before I step off my soap box and put on my flame suit: I work with students. I live near a college town. I greatly enjoy spending time in the college town after hours. But my job requires me to acknowledge my position even when I am on my own social time. If I am in a situation where I might encounter the students that I work with, I cannot act sloppily and lose sight of the fact that I am a role model both inside and outside of work. Is it truly fair that those college students can go out to bars in skimpy outfits and get sloppily drunk and not have to worry about a thing in the world except for their own dignity, while I (who am the same age as many of those students) cannot act in that manner? No, it is not fair at all. But it comes with the territory and I understand and accept why it isn't "fair." Quite frankly, I never acted that way to begin with, but the fact of the matter is that fair is not always the best way to go about things.
Eh, I think it's fair. You chose to accept this job. This is something you chose to accept with it. It's also not the same thing at all. You knowingly accepted a job where you would have to keep up appearances at all times. Somebody didn't choose to get attacked by a dog on their walk.