On the YouTube PC site users are permitted to skip pre-roll ads after 5 seconds. This is a brilliant compromise between the need to better monetize YouTube video streams and Google's general commitment to the user experience and performance-based ads.
If users don't like the ads they skip; if they're interested they watch. The advertiser only pays for those who watch the ad after the initial 5 seconds.
It's a great system and Google has now extended it to mobile YouTube video. Google argues the approach is better for everyone and advertisers get much more value by allowing consumers to self-select the ads they watch:
With TrueView, we’ve developed a model where user engagement matters -- people can skip ads they aren’t interested in after five seconds. Giving viewers choice over ads they watch has led to a better, more engaged viewing experience, benefiting the entire YouTube community of users, advertisers, and content creators.
The argument is persuasive to me. It also forces creative types in agencies to really work to make ads more interesting and entertaining. The epitome of that is the previous Old Spice campaign ("The man your man could smell like"), which was a huge "viral" success.
In mobile, ads are either relevant, entertaining or their opposites. Forcing a broadcast, "interruption" model on mobile users doesn't make much sense. You'll just annoy or alienate your audience. Hopefully other mobile video ad providers will follow Google's lead; however I doubt it.