[steerpike]

I'm afraid that even at the best of times those three specific things are very poor foundations on which to build web applications.

Consider "1. seated close 2. relatively large screen 3. precise mouse" in the context of (what should be your very first imaginary user): a search bot. Not one of them make sense and they don't make much more sense if you expand your users beyond your very, very limited set.

Consider also: vision impaired users, users without the mechanical ability to use a mouse, or any number of use cases with accessibility issues.

Personally I think the best use case in order to begin thinking about design for the web begins with: universal access to information. Every design, UX and technical decision should flow from that basic principle.