Well, at least a reason: in Snow Leopard Apple wants to allow menu items to trigger without any modifiers at all.
Thanks for the clarification... I have to say it's bad news for my workflow... I've been going crazy the last couple of days... It's so ingrained in my system... Plus, trying to get used to it, I keep on hitting command + # key and switch tab instead... grrr...
At least I know it's because of Snow Leopard now... so I'll do some kung fu training to get used to it... :'(