To be fair, it's not just HTML, "Touch Up Inside" is the usual button press event to subscribe to on iOS/macOS, and to my personal knowledge this has been true on iOS from day 1 (unsure about macOS or at least NeXTSTeP), so there is an argument that it is at least somewhat normalized, though your point about it not matching up with most IRL buttons makes sense.
However it's also worth noting that IRL buttons tend to require more than a feather's touch to detect a press, whereas there is no such margin on monitors/pointing devices.
However it's also worth noting that IRL buttons tend to require more than a feather's touch to detect a press, whereas there is no such margin on monitors/pointing devices.