She's written all of her hit songs so she made a lot of profit off them. Rihanna doesn't really have any writing credits to her name so she doesn't make much money off of hit songs. Plus Katy has a lot of business ventures.
Basically, the 360 is an exclusive recording contract between a record company and an artist in which, in addition to monies from sales of the artist’s recorded music, the label shares in other income streams such as touring and live performance, merchandise, endorsements, appearances in movies and TV, and if the artist also writes songs, publishing.
so she gets bigger $$ than most gals. i think katy managed to dodge that cuz she got dropped multiple times so she knew the ins n outs before signing a deal with capitol so ya
Also I think Rihanna's first 3 albums were some sort of 360 thing. Ultimately it worked for her career today but I dont think she made much money during that time
Katy writes all her songs and she has monstrous digital sales so she is making a lot of money, plus she has had big endorsements like Cover girl and see get's a big cut from her album sales since she has her publishing. Rihanna rarely if ever has writing credits and most of her money comes from her endorsements and tours.