Yeah, for the つらい (turai) on "Prisoner of Love", it was probably done to enunciate the emphasis on the sung note. If you've ever been in choir, chances are likely that your instructor paddled everyone to death about the importance of "strong consonants" to lead into a full vowel sound (to maximize the "singing" effect on the sound).
I've heard Utada speak in interviews, and she doesn't speak like that. Neither does BoA, I don't think.
It's quite common for artists (not only Japanese) to enunciate and emphasize consonants and swerve vowels into "pure vowels" when they sing. I.E. when you sing in English, classically trained instructors will always tell you to sing as if you have a Dracula accent XD (because that leads to less diphthongs and more "pure vowels"). Also, there are drills that a lot of singers do before performing where they go through a list of consonants and make very harsh renditions, to get their "kicked up consonant" sound going.
But in spoken Japanese, the ら is much more like a "rah" than a "lah". It's only in singing that I've heard it (and very often) enunciated more towards a "lah".
["lah" will get you into a "pure vowel" much more quickly than "rah"].
Edited by Junichiro, 13 May 2009 - 10:15 AM.