What a "majority of web sites" are doing is also completely irrelevant. If the standard says that it's a thing that you can do, and the standard says which behaviour the other party has to implement, and you are the only person on the planet to do this thing, the other party is still at fault if they implemented something else.

The whole idea of writing standards is completely useless if you can not rely on what a standard says. If something conforms to a standard, that guarantees that if you also conform to the standard, you will be able to interoperate with it. That is the whole point of writing standards. If either party does not conform to the standard, there is no value to the standard in the first place. If you are supposed to know what some random people consider sane, or the implementation details of everything that you want to interoperate with, and build your stuff for that, then you don't need a standard. The whole reason for writing standards is to eliminate the gigantic overhead and friction of that approach and to enable everyone to instead read only one document to ensure interoperability. All of that becomes worthless when you implement what you think is sane over what the standard says.