From my point-of-view, the difference is not in the content or placement, but rather in the (false) sense of control that permeates most advertising decisions today.
Advertisers are accostomed to control: when the Napalm photo was published (I was 16 at the time) the magazine had complete control over the content, and the advertiser had complete control over placement, at least as far as deciding which publication and where its ads would appear. And yes, some advertisers did refuse to advertise in some publications.
Control over the publication is absent on YouTube; control over placement is crumbling as well as copied commercials increasingly show up in places the advertiser never planned. That (unplanned) impression...is still an impression.
Going further, some of the related comments to the above post suggest that "mass adoption will never happen without control. Ridiculous. As Milennial consumers continue to shift from TV and toward YouTube...and Milennial media planners and CMOs increasingy make the placement decisions...mass adoption will most certainly happen. Get used to seeing Chevrolet, Johnson & Johnson, and Wal-Mart right next to Brittany and Eminem....even if the latter still won't stock the CDs.