I suppose if you are using 24VDC and connecting the 0VDC to ground then you do not have to use a ground terminal. A standard terminal could be used and then in theory there is still only one point to ground. However you would still have the same consideration for the incoming voltage to the power supply that the 24VDC is derived from.
Interesting stuff, I have recently been looking into this. With regards to what arj3090 said - if it is unsafe to leave 0VDC ungrounded then can someone explain why it is not against regulations etc?