Not knowing the latest hit movie characters, not watching cartoons on tv, not listening to pop music - none of that caused an issue in meeting and making friend when my kids went to school.
It actually did make a difference to my DD in preschool. She had not been exposed to any Disney anything, and the pack of girls her age played Disney princesses every single day. Admittedly, that is an age when girls may be monomaniacal on this subject, and it did not help that DD was a) not interested and b) socially immature. However, we got her some Disney princess books from the library so she could at least understand what they were talking about, and it helped. (I remember my little birdwatcher initially thought Ariel was named "Oriole.")
Likewise, DS6 goes over to other boys' houses and it's slightly mortifying/weird to him that he does not know how to play any Xbox/Nintendo/whatever games. BTW, I haven't caved on this, but it has come up for him. So, at least he plays Angry Birds and some other stuff like that and has SOME knowledge.
It might matter less if one's children are highly socially skilled. IDK. Both of my kids are pretty well-liked, but one is quirkier and more out there. I am very sympathetic to the needs of families with, for instance, kids who are either ASD or ASD-ish, for whom Legos or Minecraft or whatever is such an important point of entry. So, I don't think should be dismissed. Of course, don't force it on a kid.
I mean, if you met us in real life, you'd see--we're totally fringey too.
