CLUSTER, using SHARE UPDATE EXCLUSIVE lock?

Hello,

CLUSTER uses an ACCESS EXCLUSIVE lock. Why does it forbid concurrent reads?
Florian G. Pflug, on a post ( 
http://archives.postgresql.org/pgsql-hackers/2007-02/msg00081.php ) 
suggested that there were no way to let the old entry until the command 
commit.
I would like Cluster to create a new table, copying old values to this 
one, then delete the old one. This would allow Cluster to work with a 
share update exlusive lock, in order to allow reading the table while 
cluster is working.

How does Cluster actually works? Why making a Cluster command less 
restrictive isn't even in the TO-list?

Best regards,
Jonathan Scher