Do modern web applications need warning states?

I'm just curious about the system status in the modern web app design. In some old windows applications, they have warning(yellow colored), error(red colored) and success (green colored). In the modern web design, I haven't seen any warning status been used explicitly (except some dialog). So I was wondering if the warning status still make sense today? If no, what can be done to minimize the warning if such application goes to web? Thanks.