"My name is Stefani Joanne Angelina Germanotta, also known as Lady Gaga." I think that's the first time I've heard her say her real name. 
 
Maybe there are more important causes out there, but there's probably a million of them, and she can't go out and try to solve every one of them.  If everyone embraced ONE cause they were passionate about, that would make a big difference. 
As for can a pop star make a difference, yes: 
http://www.politicsdaily.com/2010/09...lshare_twitter