Part of the problem is The US Government (and UK Government) use the "2% rule" on their websites and only officially support 98%.

I mentioned 3 years ago that Firefox at 2.2% is dangerously close the being unsupported on government websites, and at this point it's now at 1.9%.

https://news.ycombinator.com/item?id=36776603

https://analytics.usa.gov/ says "There were 1.66 billion sessions in the last 30 days." - so 2% is 33 million sessions if I did my math right.

Yeah, this is sort of the problem with a percentage-based approach. You are better with a "pick the top 3 implementations" in most cases - that bags you Webkit, Blink, and Gecko in the browser example, and since we're ignoring the long-tail in either case, that's probably good enough