It's not the score.. it's the value of the troops you've killed, so makes every sense to have it in currency... or am I missing something?
It is the score that you've killed that is in the stat, not the value of the troops. So if you kill a guy who is 5 bil score and he goes down to 1 bil score, you have killed 4 bil score. And that's what the stats page will show.
Also, I noticed this quite a while ago:
Value of enemies disabled: £1,049,035,900 100
Value of enemies distracted: £508,256,025 134
Value of enemies killed: £19,772,377,875 3
Value of enemies bribed: £0 150
Total score damage done to enemies: £20,453,832,035 6
Value of friendlies had disabled: £1,372,946,836 161
Value of friendlies had distracted: £3,798,286,765 113
Value of friendlies had killed: £2,538,172,928 145
Value of friendlies had bribed: £323,706,461 56
Total score damage had done to: 3,521,027,552 114
All the stats there are done in £ except for the "total score damage had done to" one, which is in score. I don't know why, but it's been like that since last round at least.