Its a bit of an old wives tale. In the Falklands they took hundreds. It started many, many years agooooo..... (mist swirls round and my voice echos into the distance..) When Britain started to use Gurkhas as part of the British Army (The Indian army has them too) they were paid a very meagre wage (still are). To suppliment this, they were paid a "bounty" for every enemy soldier they killed. The way they used to prove they had killed someone was to cut of the dead mans ear and present it to the sargent major for payment...however, they soon cottoned on to the fact they could get two bounties per body (two ears)...so, it was made that it was only the left ear that would be paid for!!! However, this practice stopped at the end of WW2...and they started to take prisoners instead of ears.
The officers mess in Brunei has hundreds of dried Japanese ears threaded on silver braid hanging around the walls....Nice..lol