I guess this boils down to what is my goal. Here's two plausible goals from my perspective. I go to DDG and ask for it to give me a sample of some sources from which I could find the weather. This is a traditional search. Or, I could go to DDG and ask it for the current weather. This is what I really want.
There's no scenario in which I already know which weather source I want to use, memorize its ! command, navigate to DDG, then enter that ! command. That's too many jumps. If I want the weather from weather underground or whatever, why would I ever go to DDG to start with?
I have DDG as my default search engine, so I just type "!wu 01234" in my address bar. This basically skips the DDG navigation and UI entirely. I like this type of shortcut for Wikipedia and IMDB too.
Anyway this is just a workaround for when the weather infobox doesn't automatically show up in the DDG UI, which it normally does.
There's no scenario in which I already know which weather source I want to use, memorize its ! command, navigate to DDG, then enter that ! command. That's too many jumps. If I want the weather from weather underground or whatever, why would I ever go to DDG to start with?