Is News.app a resource hog for anybody else?
In essence, it's a 'multimedia' app, like a browser with many tabs open.
Every new page/report you open will load new content. That will stay in RAM until you quit.
They only way to keep its footprint down would be to only read the headlines, or quit after every report you open - which is hardly practical.
The Mac will handle memory usage quite well on its own. If the app really does start to use up too much RAM, then earlier pages will be released back to the memory pool, so the it can be used for something else.