ayu instrumentals

[mirrorcleworld]

how come the instrumentals on ayu's singles have lapses of ayu's voice still on them? i find it really annoying most of the time since i enjoy instrumentals a lot.
i've also noticed that some other artist's "original karaoke's" and "instrumentals" also have these leftover voices, like hikki's singles for example.

but with other's like namie's, aoyama thelma's, and SoulJa's (i not sure you've ever heard of him, -koko ni iru yo anyone?-) instrumentals have no voices popping out at random whatsoever, they only have them VERY RARELY like only 1 out of a 100 or something (i'm not sure)

so does anybody here know why is that?

[Ayumi_lover]

on ayu's instrumentals there is no ayu voice but they left backvocals so it would be easier for you to sing along the song. And if you would like to perform the song in public I think it would be better to have backvocals. Don't you think so?)

[nanakopy87]

this is why they state there 'instrumental~original mix~'?
i realize those who write 'instrumental' only are 100% only has music(without back vocal etc)