groupinstall functionality change from 2.6 to 3.x?

I notice that my RHEL4 clients running yum 2.4.2 do not update RPMs  
with a groupinstall, whereas my FC6 clients do updates with the  
groupinstall with yum 3.0.3.
I have to use groupupdate to get updates to run under 2.4.2. Not a  
big problem, but I have a script that runs groupinstall and I was  
using it (hoping to) to perform both installs and updates from the  
same repo, with the same "yum groupinstall" invocation.

Can you verify that groupinstall inherited the update feature after 2.6?

Thanks,
Wayne Sweatt