In the case of web standards, the null hypothesis is "no new API" rather than "make something that works only on top of this specific native API". For the web, the latter is not even the default assumption once you've decided something needs to be added. The web is cross-platform by design.
>In the case of web standards, the null hypothesis is "no new API"
Thanks to Apple's bone-headed decision to not support Vulkan, this is what it has come down for me when it comes to graphical APIs. For me it's either "no new graphical APIs, keep being forced to use OpenGL" or "drop macOS/iOS support".