Taking it out of USD and changing the units around (even though it's just dropping a decimal point) mentally disassociates 'Amazon Coins' from USD. Microsoft goes even further on the Xbox, 1 USD (+ local sales tax) buys 80 MSP; so it takes a moment to realize an 800 MSP game is actually $10.
I've seen this many other places. They seem to intentionally choose hard-to-calculate multiples. No one ever sets them at 10 or 100 to the dollar.
They are less abstract. My 8 year old's iTunes balance has a $ in front of it. She understands it.
It is more like a credit balance though, and not a virtual currency. Purposefully, I imagine, to make accounting/taxes more straightforward.
At least it's a (nearly) 1:1 rate.
This seems to be as well, just multiply the USD amount by 100 or divide the Amazon Coin amount by 100.