I don’t think that this issue is wholly with Safari. And I think it’s a little unfair for the article to imply so.
Browsers these days are complex beasts; they need to render (X)HTML and CSS properly (or not…), provide supporting frameworks for who knows how many mimetypes and plugins, run multiple tabs, be extensible so that addons can be… well… added on. It doesn’t surprise me in the least that today’s browsers have memory management issues. And when addon authors inadvertently don’t properly manage thread and memory safety, frankly, you’re doomed.
I’ve been having massive issues with Firefox lately – beachball of death, insanely slow page load times, streaming at a snail’s pace. That kind of thing. I apparently solved the Firefox issues this morning, however, by removing several addons I wasn’t really using. Now, it seems to go whoosh.