This sounds kinda nitpicky but I think it's an important distinction. We're talking about the web, not the internet, right? Or is hcaptcha also used for iOS apps, Android apps, etc.?
A client (whether browser, CLI, phone app, bot or anything else) making resource requests identified by a URL to an HTTP server is as "web" as it gets.
The reason you see fewer capchas on iOS and Android is that it is a lot harder to automate them for spam, that's all.
> The Internet carries a vast range of information resources and services, such as the inter-linked hypertext documents and applications of the World Wide Web (WWW), electronic mail, telephony, and file sharing.
Edit: but to be fair I totally brought this semantics debate upon myself by raising the question of the difference between the web and the internet. Not sure why I took on a whiny tone about that, haha