question about yum update, graphics packages

[Peter Horst]

I just tried my first 'yum update'.  The list of packages to be updated 
included 'gtk2' and 'mesa-libGL', but the system that I'm updating was 
installed without an X server.  Aren't those graphics packages?

I am just curious as to why they would have been included during the 
install process.  My impression was that 'yum update' would only update 
packages that are currently installed on the machine - is this correct?  
PS I'm not an anti-GUI fanatic, I'm just curious :-)

Thanks very much...