this is because browsers have very sophisticated algorithms to detect the encoding because this was such a frequent issue. (and yes, UTF-8 adoption/support has been growing, which also helps)
being German and working in a multi-national company, i can confirm it is still very much an issue with software that doesn't handle this. Excel is one of the worst offenders, document corruption is rife especially when going between Excel on Windows and Excel for Mac. this is because Excel doesn't to UTF-8 as default for legacy reasons (I think), but also either doesn't have encoding detection or has very bad encoding detection.
being German and working in a multi-national company, i can confirm it is still very much an issue with software that doesn't handle this. Excel is one of the worst offenders, document corruption is rife especially when going between Excel on Windows and Excel for Mac. this is because Excel doesn't to UTF-8 as default for legacy reasons (I think), but also either doesn't have encoding detection or has very bad encoding detection.