@lxo modern webmasters don't "shift" the computing costs, they use client-side processing and caching to avoid transferring redundant data which the user may not really need and that would only hog the service back-end. Here, JavaScript is used to guarantee a fast and smooth service for everyone.
Websites change frequently, so amateur automations can be dangerous and unreliable. If the webmaster wants to allow automation, then the website will offer public APIs.
CC: @tennoseremel @quasi