>What do you do when that happens on your laptop? You close the page and move on.

No, I proactively install apps such as "Click to flash" and the like to make sure this DOES NOT happen on my laptop.

>Why does it need to be any different on your mobile/tablet? I assume the battery cost of 2 seconds of video loading/playing once in a long time is negligible.

Because I could be anywhere surfing with my mobile/tablet, in the dentist's office or even in a meeting. I don't want pages to jump at me with video I have not requested. Ever.

And I don't want web marketers to assume anything about the battery life cost of their actions on MY devices.