Money in a closed ecosystem

[Sarad AV]

Came across this interview of an ATM machine in Antartica

http://www.needcoffee.com/2010/01/12/antarctica-atm-interview/

Here is a snippet of the Q&A session from the interview:
"
DP: You know, that is a very good question, and you're right it is
challenging--certainly makes for a long commute for our servicers. I'm kidding
thereb&tongue-in-cheekb& No, actually, what we do--first of all, the cash on
the ice is recycled. So McMurdo Station (which is the scientists' station
there on Antarctica)... any sort of venue, the cash is all recycled, and so
there's no cash vendor that has to go down all the time to a regular ATM to
replenish the cash volume.

W: Rightb&there's only so many places one can run with cash down there, I
assume.
"

That brings us to the obvious question, why not use something like a debit
card hooked to a central network? Why does hard currency have to flow? Will
not the time and effort be far lesser, in case of the former?

Thanks,
Sarad.