And just exactly why would they want to do this?

I'm a little uncertain about the long term future of this effort.   Knowing what your cash position is instantly is good, but is this really the way to do it?

Almost every tube station in London shows adverts for contactless technology.  Credit and debit card usage is increasing (at the expensive of cash) and larger stores seem to have faster and faster processing times. 

From what I've heard, the end of cash is nigh.  Well, that's a little dramatic, I admit.  Certainly, for small purchases, particularly out of store, cash will still have a place for a while yet.   But in the retail environment, it seems like these are perfect places for non-cash solutions to be rolled out.  

Underground travellers in London have had no problems migrating to Oyster.   It has obvious benefits; even if we were "forced" to change by the price increases for non-Oyster use, it was great once we got there.   The new Barclaycard with Oyster, cashless, and credit capability sounds like a beauty to me. 

I can see a time in the near future when retail outlets will have say, 10 check-out registers, with perhaps only two of them reserved for cash payments (there will be a big dinosaur above them to make it clear who should head there). 

Somewhere, the cash is going to have to be reconciled with the recorded takings from registers.   Contactless and card purchases don't have this problem.  

I'm afraid I don't see why a retailer investing in a new payment avenue wouldn't be better off spending their money on non-cash options.