This was also published not too long after Snow Leopard came out (August 2009), which is when Safari first split plugins out to a separate process, as long as you were running it in 64-bit mode. Before that it could bring down the whole browser, after it would only kill itself and require pages to be reloaded. So it's not like Apple wasn't doing anything about it.

Obviously a positive change in general, but the push to prioritize that and get it done must have been 99% aimed at problems caused by Flash.

And even after that was implemented, an ad crashing flash in one window would still bring down a video player in another, if I'm remembering right. Still a crappy user experience.