Perhaps it's one of those cases where a generalization is sometimes over-applied as an absolute rule.
Also, sometimes teachers make the decision that based on the level of their students, it's easier to pass something off as an absolute rule, than to potentially confuse students with all the nuances of when it's okay to break the 'rule'. Of course, if you do that, then you need to come back and explain exceptions at a later date.
I can't say if that's her approach, or she honestly isn't aware that there are exceptions. She does address the McDonalds' slogan at about
1:51, passing it off as "creative license".
Note that one commenter who claims to be a teacher states that he disagrees with her information. There are many other commenters asking about exceptions as well, and she doesn't respond to those questions in the comments.