BGP neighborship problem

Hi fellas,

I have a simple topology R1----------------------------R2 R1 is
forming neighbourship with R2's loopback and viceversa. I have a default
route configured to reach loopback.
Why BGP cant form a neighbourship with a peer with a default route? Why it
needs a unicast exact route to form a peer?
What is the logic behind this ? Can anyone explain me the logic?

-- 
With Warmest Regards,
CCIE KID
CCIE#29992 (Security)
Blogs and organic groups at http://www.ccie.net