SVI Interfaces has same MAC

Hi fellas,

I find different SVI's has same MAC address .Like SVI for Vlan 10 and SVI
for Vlan 20 has same virtual MAC address. I want to know the reason why they
both have same MAC address. Is there any reason behind it to do this kind of
design. This is my config

int vlan 10
ip add 10.1.1.1 255.255.255.0

int vlan 20
ip add 20.1.1.1 255.255.255.0

and I find same virtual MAC address when i do sh ip int vlan

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