I've never heard of her before the Travolta incident either.

There was a thread about it a while back and I practically got reamed out for saying she wasnt famous!
But she IS famous, as is Taye Diggs. However, being famous doesn't nec. mean that EVERYONE has to have heard of you, just that a really substantial number of people have, because you are notable enough to consistently be on the radar of your country's mainsteam press for your accomplishments.
Infamy actually is more likely to draw more widespread attention than true fame, so the average artist probably wouldn't really want to be so well known that nearly everyone everywhere would recognize his name. That tends to be the sorry privilege of the Hitlers of the world.
There is a joke in
Good Will Hunting that highlights the relative nature of fame. In a discussion regarding fame with a respected mathematician colleague, Robin Williams' psychologist character mentions that "in the 60's, a young man graduated from the University of Michigan, did some brilliant work in mathematics, specifically bounded harmonic functions. Then he went to Berkekey, was assistant professor. Then he moved to Montana, blew the competition away." The colleague doesn't recognize the description and asks the young prodigy's name. Williams tells him the name is Ted Kaczynski. The mathematician says he has never heard of him. So Williams asks the bartender who Ted Kaczynski is, and of course, the bartender instantly replies that he was the Unabomber. The point being that no mathematician, no matter how brilliant, is ever going to be as well known to the average man on the street as a convicted mad bomber will be.
The expectation that posters here would know who Menzel is isn't all that odd, given what we all have in common: we are Disney fans. Menzel has worked for Disney or ABC on several projects.