Why doesn't Twitter and Google API documentation encode ampersands in URLs?

Question

I have read I should encode my ampersands as & in HTML.
However numerous code samples from respected companies somehow forget

Answer 1

Is there any real benefit from not escaping ampersand in links?

It saves a few keystrokes.

Is this related to browser quirks?

No

Is this just a mistake in documentation?

Yes

Is there a reason API documentation by respectable companies often violates this rule?

Ignorance and/or laziness. Browsers perform error recovery so they either don't notice the errors or they don't care. The documentation probably isn't written by their best experts.