To some extent it's fallen off because we've reached (somewhat) of a plateau. Originally all mining was done using CPU resources, but the first big jump up in hashrate came as folks started to figure out GPU mining. As GPU mining grew more popular, the hard core geeks started looking at FPGAs and eventually we made it to full blown ASIC miners. The last big explosion of hashrate was driven by the bulk of miners adopting ASIC hardware of one flavor or another. Now that the majority of miners are on SHA256 ASICs the only gains to be made are by shrinking the die and increasing the transistor count but even those hard earned gains are going to be quickly diminished as ASIC hardware "catches up" to Moore's law.
As for hash power leaving the network, if you are mining as a business then you are 100% at the mercy of 1) how much you pay for electricity and 2) market price for coins. Given how many schemes exist for stealing either computing power or electricity I imagine the margins will converge on a negative number at a large enough scale.
So it seems the idea is you spend $400 to get a Bitcoin machine and then you have 25 cents to spend each day on news articles, apps or music in some effortless or 'identityless' way.
My theory is that their real motivation is to ensure that there continues to be a robust mining ecosystem when the block reward falls off to the point that nobody wants to mine anymore without high transaction fees. So they proliferate a bunch of low cost mining gadgets that people will use primarily for the convenience it offers in making micropayments and in verifying identity, while they also do mining to ensure the health of the network but not actually make any significant money for the owner.
This would be the first iteration of their first gadget, which isn't cheap yet but could be if volumes are high enough, and future iterations would be cheaper and better.
The identity feature is my speculation based on tweets by the CEO about the need for better identity solutions and the enormous market for solving identity fraud problems. Not sure how a gadget like this addresses that but I think it is part of their plan.
If you figure 0.16 Joules / gigahash and 100 gigahash/second, you'd be looking at about 0.39 kwh / day. At $0.10/kwh, you'd be spending about $0.04/day on power.
If the past is any guide, that quarter a day will rapidly decay towards 0 as the global hashrate continues to grow.