Looking at the CAA MMEL, a single engine or APU equipped generator may be U/S for non-ETOPS flights, provided that all indications on the alternate are normal, all busses can be powered and the faulty item is rectified within three days.
Conjecting wildly, one can see a Captain seeing that if he took the aircraft, the generator wouldn't be replaced within the 3 day interval - and his management feeling otherwise. (Which, just to repeat, doesn't change the fact that the Captain has responsibility to accept or decline the aircraft.)
G
AC Power Supply Note: All indicators and warnings may
be inoperative on a channel
considered inoperative.
Engine Driven Generator
Channels (IDG, GCU, Line
Contractor)
Except for ETOPS operations, one
may be inoperative provided:
(a) APU and APU driven generator
channels are operative and used
throughout the duration of the flight,
(b) All busses can be powered,
(c) Indications and warnings for the
remaining engine, and APU driven
generator channels are operative, and
(d) Repairs or replacements are carried
out within three calendar days.
Note: No further alleviation is given.
APU Driven Generator Channel
Except for ETOPS operations beyond
120 minutes, may be inoperative provided:
(a) The STBY generator is operative, and
(b) Repairs or replacements are carried
out within three calendar days.
(from
http://www.caa.co.uk/docs/33/SRG_ACP_A300-600_REV3A.PDF , page 31)