That's because Stable, being stable, gets updated only extremely rarely -- roughly once every two months in the case of the previous release, and even then it's more "move security updates into the main tree and rebuild the images" than adding anything new. Adding new stuff is what testing and unstable are for.
Security updates for the Stable distribution are updated via
deb http://security.debian.org/ stable/updates main contrib non-free
and for more volatile packages you should also add
deb http://cdn.debian.net/debian/ squeeze-updates main contrib non-free
Useful relevant information from Debian can be found at http://wiki.debian.org/StableUpdates
EDIT: The first point release update happened today, March 19th. I'm guessing they'll try to stick to a bimonthly schedule, with some elasticity to keep to the Debian standards of reliability and stability.