Using "that would be" and certainty

Position   Mon Dec 19, 2005 11:20 am GMT
Below, is the speaker B sure of who the person is?

A: Who's that woman over there?

B: That would be Julia Roberts.
Guest   Mon Dec 19, 2005 11:27 am GMT
Yep
Guest   Mon Dec 19, 2005 2:32 pm GMT
Why does the speaker say "would be" and not "will be" or "is"?