Re: TL:DR Security by obscurity is good for you. Don't bother your silliy heads about such things
People are (deliberately?) missing Google's point here.
"Microwaves and cars are physical devices."
Not completely. Most new models depend on software to some major degree.
"They have very clearly defined properties and it's usually pretty obvious when they fail"
"Microwave does not cook food put in it? Not working."
That's analogous to "Google returns nothing when I search for something".
That is, of course, not the point. The issue is that people believe that Google is returning results that are not optimal to the users' requirements, but are relevant enough that most don't know or care.
To use the microwave analogy, this is like you telling it that you want to cook at 70% power for 3 minutes, but internal design means that it actually cooks at 74% for 2 minutes 54 seconds to conserve power or to optimise some other internal process. You don't need to know or care, so long as you get sufficiently heated food.
"I especially like the "And it could affect small startups.""
You don't think that being required to publicly reveal algorithms would effect them as much as established players?
"Google is built on being the biggest search engine on the planet by a large margin."
It didn't start that way, and has got to be there currently largely because of the algorithms it uses.