I rapidly re-checked an account of Rorke'sDrift battle, and you are right (at least partly <img src="images/graemlins/grin.gif" alt="" />) : the british soldiers made a stand at this place to prevent/delay the crossing of the river by the Zulu and the then possible invasion of the Natal province.

OTOH ......
I wouldn't say they had "ample time" to retreat :
they were warned of the approching Zulu army by survivors of the defeated british task force (1500 "red tunics" killed at the Isandlawana battle, january, 22nd 1879).
This same day, at about 16:30, Zulu forces attacked the improvised "strong point".
That means, had the british forces at Rorke's Drift choosen to retreat (slowed down with their wounded), they would have been only a few hours ahead the Zulu. They then certainly would have been catched up in the open and massacred.

This being said, I agree with the rest of your post. And especially about [this willingness to spend lives like loose change] ...
AFAIK, the same thing happened in numerous other places, in Vietnam, for instance.

OTOH, a strong point as Rorke's Drift place, somehow limited the advantages of the comparatively huge numbers of Zulu.
It was physically impossible for them to attack all together ; but they could launch almost countless assaults....
Look at the Cameron battle. Or Alamo.
Nowadays, a bomb from an aircraft would "solve" these "problems".
But then, it was more "handcrafted" (?) and the assailant send troops until the defenders run out of ammunition and/or stamina....



Alain