Netflix is running ads, which it insists aren’t ads
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However, the ad trial is likely meant to open the door to new pricing options that do more than tweak the number of simultaneous streams. Netflix could offset price hikes (and undercut streaming rivals) by launching a cheaper, ad-supported tier; alternately, it could compensate for slowing growth by asking you to pay more for ad-free viewing.
Sure, there are previews and other types of bonus material on DVD/Bluray discs, but they can be easily skipped with the method I use to watch them.