Yeah, Javascript must be really confusing to have so many people asking questions about it :-).
I jest, but seriously, popularity of a tag on StackOverflow should be used to determine one thing: popularity of a tag on StackOverflow. There are more important factors influencing a subject's popularity on SO than its overall popularity. A big factor is where the community around the technology tends to congregate. Many projects (like Guava: http://code.google.com/p/guava-libraries/) officially endorse StackOverflow as the place to ask questions, because the maintainers and experts will be monitoring SO. That will have an inflating impact on its relative popularity.
Indeed, mega-monsters like C++ and Python are old enough that Google sends people away from SO to more traditional old books and blog posts which already have most questions answered.
I jest, but seriously, popularity of a tag on StackOverflow should be used to determine one thing: popularity of a tag on StackOverflow. There are more important factors influencing a subject's popularity on SO than its overall popularity. A big factor is where the community around the technology tends to congregate. Many projects (like Guava: http://code.google.com/p/guava-libraries/) officially endorse StackOverflow as the place to ask questions, because the maintainers and experts will be monitoring SO. That will have an inflating impact on its relative popularity.