Here is the definition of "jhai" from publicity during the promotion of Let It Die:
"a detached manner of singing especially suited to very emotional material. The emotion is underplayed, never quite lets go and leaves room for the listener to crawl inside."
What is interesting is that, of course, Feist is not the only singer who does this. Our friend Steven Patrick Morrissey also employs similar techniques of vocal delivery.
("Jhai" definition found at the link above - just click on the title of this blog entry)