Rihanna has popularity for other reasons than her music. And besides that you said record sales isn't a good measurement, record sales ≠ first week record sales. Rihanna's last album has sold 980k in the states (still counting) and 3-4 million worldwide. She has sold over 25 million with 6 albums world wide (don't forget that she's not even an American artist). She sold out 9 shows in a row in the same arena in London. But because of this iTunes thing, a lot of fans only buy the songs they like that's why Rihanna has sold 60 million singles or whatever the fukk.
I know Rihanna is popular for other reasons than her record sales, which I why I said record sales aren't always a good measure of popularity...
First week record sales are record sales... a lot of people like to bring that up when talking about how popular one artist is compared to the next. "Jeezy is more popular than Ross because he sold more first week" etc etc. I guess I should have said that first week record sales don't mean shyt.