Youtube does provide info on which portions of videos are the most watched - while most advertisers aren't the kind of people that do due diligence, quite a few of the big management groups have started introducing contracts that base payout for sponsor reads off of actual watch count. AFAIK it hasn't made too much of a difference yet (though channels with high skip-counts are less likely to be given the decent sponsor deals) but if youtube makes the analytics easier to access it probably will have a pretty big impact.