I dunno, thats how the market is I suppose. Probably because of how the single release is handled; build up on radio for about a month then big debut sales then fall quite quickly. It's not been happening as much nowadays I dont think, but last summer it happened LOTS
Im not gonna use that website as a source. I already have a feed saved which i can use (which says gaga is #3) and also the actual itunes store program which says gaga is #3 aswell