The only relevant Web standard in every era is "does it work in the browser most people are using". So Netscape in 1995, IE in 2000, Chrome today. That's just the reality, unless you'd rather lose money doing Web development.
That really depends on the values of the business in question. Some would look at that differently, and argue that developing to wider standards and testing on other platforms is an investment in quality and longevity.
Fully agree with this. I know people who were developing 3G/4G base stations at Ericsson, and as they say: the only right way to check if implementation is correct - to test if your phone connects to it or not.