Since Baez grew in NY and sings in English, I guess she´s got limited reach in Mexico.
My comparison of Sosa with Baez comes from their shared folk roots and human rights activism and progressive political involvement.
It´s 11:40pm and people are still entering the Congress building to give their last goodbye to Mercedes Sosa, that speaks volumes about her popularity down here. She was also very popular in Chile, Brazil and throughout western Europe.
She recorded La Maza with Shakira http://www.youtube.com/watch?v=zXBze4zysYk
And lately she even made inroads in Israel, singing in Hebrew
http://www.youtube.com/watch?v=cI_dYpjwC4A
Not bad for a 74 year old self-titled proud communist!
FC PS: Wait, look what I found... Baez and Sosa... with English subtitles... http://www.youtube.com/watch?v=wze9r6JvXEY