what the MEL says
Luftis is right George,
The MEL says:
29-11-02-01 No. 1 or No. 4 Demand
Pumps
One may be inoperative deactivated
provided:
a) VMCG is increased by 5 kts.,
b) Gear down climb limited take-off weight
limitation is observed.
c) Runway length/obstacle limited weight
must be reduced by 50,000 kg, and
d) Demand pumps 2 and 3 operate
normally.
So it is VmgGround.
As to why, I don't know either.
Bodygear steering cuts out above 20 kts, so that can hardly be a factor.
If credit were given for nosewheel steering, it would only apply to Hyd dem pump 1, the hydr system powering the nosegear steering.