Steve,

Electrically the grounds are connected but are seperate to prevent earth loops and induced
noise from voltage and current transients.
I.E. they terminate at one central point within the equipment.

As for the two types, there are two possibilites that I have come across before....

1) 'RGB' and 'component' are names given to the way the signals are grouped but
are essentially the same electrically but may have different connectors.

2) Components refer to all video signals being seperated. I.E their component/signal form.
Seperate H sync, V sync, Red, Blue, Green carrying pure information etc...
As opposed to ...
Composite sync - H sync and V sync merged - (do not confuse with composite video)
and/or sync signals merged with colour signals.