What does influential mean?

I read MSN's list of most influential men and women of 2009, and since this is a music blog, it struck me that they listed Michael Jackson and Taylor Swift to the list.  This got me to thinking: when you compose a list of influential people for a year, what do you mean by "influential"?  Did the person do something that took their area pf expertise in a new direction?  Or did they just capture a lot of attention for 12 months? 

When it comes to music there, seems to be a double standard.  For influential people in the area of politics, or finance, or science, ususally that person reveals something that was before unknown.  But with musicians, it seems that whoever captured the most attention gets the nod.  Michael Jackson did through his death, and Talow Swift because of the success she had as a young performer.  In my opinion, neither one did anything that hadn't been done before, so why are they considered influential?  I know Taylor did a lot of charity work this past year, but so do a lot of people, and you don't see them listed.