you can't compare sales with boy bands, especially the ones under johnny management. first of all, it's KAT-TUN's debut single (i dunno why they didn't release anything during the past 4 or 5 years tho..). Secondly, young girls willing to spend a lot of money on boy groups. Thirdly, they have 7 different covers (6 limited, 1 normal). Each member of the group got a chance to stand in the middle of each cover (and there're 6, so that's why 6 limited editions). Last but not the least, they have done good strategy this time... Releasing the first single, first album, and a DVD at the same time... No wonder they can get a lot of sales. (it's good to see oricon bringing up a history tho.. the last person getting no. 1 on those three categorys at the same time was ayu: SURREAL + Duty + concert tour 2000 A
).
If ayu's gonna make 6 different covers on CD+DVD edition, I'm sure she may be able to sell over 200K at least on the first week as well.