Since many things you do happen in web pages these days, being able to automate them is quite useful.
The tricky bit with web pages is they tend to be quite fluid, the window size changes, and the contents of the window can move around quite a lot, and the window often scrolls, so identifying elements on the page can be quite tricky.
A good solution to this issue is using an XPath, which is like a file system path, but is the path through the Document Object Model (DOM) to the desired element.
Keyboard Maestro 8 adds support for XPath in all the actions:Browser Form Actions like Set Field to Text and Click Link. The actions will generally let you select the appropriate fields or links and fill in the XPath for you.
This lets you more robustly control web pages.
Like applications, when controlling web pages, the degree of robustness depends a lot on how the web page is implemented. If it is implemented cleanly, you can control it reliably and easily. If the developers of the web site have added lots of custom bells and whistles, then controlling it may be far more difficult, and you may have to resort to UI actions.