> why is a web page different?

Web browsers on desktop operating systems initially allowed any website to play audio without any interaction required. Some websites would blast annoying audio ads as soon as you opened a page on their site. So effort was put into making it so that web browsers on desktops would only play sound after user interaction via mouse click. Later, some websites were exempted from that by some desktop web browsers, for example YouTube I think.

Even without ads, background noise that starts automatically as soon as you visit a page can be distracting and disruptive.

I’m perfectly happy that Safari on iOS does not play background audio when I have my phone in silent mode. Even when I have tapped on buttons on the page.

Silent mode is not entirely only for notifications anyway. The built-in keyboard is also silent in silent mode, whereas when silent mode is off it makes an annoying click sound for every button that you press. Likewise the builtin camera app on iOS makes a shutter sound when you take photos with silent mode off. With silent mode the camera app is silent. Same with taking screenshots. I take a lot of screenshots, and prefer that people around me don’t think I’m taking photos when I am taking a screenshot on the phone.

Meanwhile, if I open a music player app on my phone and hit play, I have made a very deliberate choice about playing sound.

All of the games on my phone I can think of are also silent in silent mode. Not sure if all games have to be silent in silent mode or not on iOS (i.e. if “can play sound in silent mode” is a special permission in iOS and if Apple disallows apps categorized as games in App Store from having that permission or not). But I like that the games I play on my phone are silent in silent mode.

There is some inconsistency indeed about what is silent or not, but I am happy with the way that it is as someone who prefers surprising silence over surprising noises from my phone when it’s in silent mode.