Actually it doesn't even seem to load most of the page in a background tab until it's focused... which is also annoying. (Or perhaps it's just the parts hidden behind 'onload' JavaScript, which these days is most of the page content.) Part of the reason for opening the tab in the background is getting the lengthy loading process out of the way while I'm reading something else.

For this reason I tend to activate the tab and then go back to what I was doing before... and then the video auto-plays.