For all the (often deserved) hate Windows gets, in particular the user space API’s, I still find the chaos incredibly exciting and an invitation to hack together all sorts of strange things in strange manners. I’m sometimes surprised by the levels of backwards compatibility and the “obsolete” technologies that still work fine.
The success of Windows to maintain backwards comparability is probably some of the inspiration for the people working on JS. Windows has demonstrated that it's possible to maintain backwards compatibility for decades.
It's not easy, and it certainly leads to annoying platform quirks, but it is possible.
The Web probably has a longer history of not breaking things, but also has a smaller feature set to keep track of than Windows.
All in all, very hard to compare. But both undoubtedly epic.