Yet somehow software developers are quick to screech that users agreed to 'license agreements' that have the same weight, right? (Words on a screen that everyone just 'clicks through blindly'.)
You can't have it both ways. Either having something show up and clicking next manifests consent or it doesn't. IE is extremely clear that DNT will be turned on and lets you opt out of doing so. Users are expressing intent by using the default settings; it isn't like it's a hidden default that they don't tell anyone about.
I don't know any developers that believe that however I've met many managers and attorneys that believe it. Common industry practices should be laid at the feet of those responsible.
Beyond licensing agreements though, people won't read instructions, disclaimers, warnings, etc. It's not just one thing, and when designing things at work one of our common points to try and make things more clear includes "people don't read" so how can we improve this.
