Lower risk, but it probably reduces income: how many people can figure out how to make a bitcoin payment? How long does it take to make a bitcoin payment? The harder it is, the more likely the target is to give up and do without.
I think their Bitcoin payment method is actually to facilitate international payments (funny in a dark way) - they also take the popular shady prepaid-debit/cash-wire service GreenDot Moneypak and I'd imagine most US victims paid up that way.
There are a couple of anecdotes on Reddit about Canadians and other non-US residents scrambling to find a physical Bitcoin storefront or Craigslist contact to pay the ransom for them since Moneypak wasn't available in their area.
I would think their C&C server sets up a random Bitcoin wallet, and waits for a deposit, then allows the private key to be retrieved the next time CryptoLocker phones home.
