It might be interesting to see the numbers for a coin using an algorithm where the mobile chip isn't at as much of an extreme disadvantage. A virus that returns anything is more attractive to the author than one that returns nothing, so despite the miniscule returns, I'd expect to see more of this.
This. I wonder how many phones would be needed to mine something like Primecoin or Bytecoin/Monero which unlike Bitcoin, can still be mined with CPUs and GPUs. These coins can then be traded for Bitcoin on an exchange. I would think that far, far less than 14 million phones would be required to earn a bitcoin that way.