In some songs Utada does sounds like Mariah to me even if I have listened to Hikki for 4 years or so now.

Especially song On and On brought Mariah to my mind at once when Hikki started singing the song. I was wondering "Why's a Mariah Carey song on this album?" and I haven't gotten used to that voice yet but I still adore the album. And yes, I'm a Mariah fan too. :p I'm not very annoyed of the comprasion of both of these artists since they are both my favourities and I love their voices.
And about singles. Here in Finland artists releases 1-2 singles off one album before it's released. They also release re-cut singles that has no remixes in, which is sad. I, for example, prefer japanese way of releasing things.