While this is true to an extent, there's a forgotten factor in the equation: Profit.
All the while there is a profit to be taken with what is perceived as a reasonable rate of return on investment people will respond to it. Unfortunately a lot of that profit is considered in £/$ etc - plus there's the obvious electricity costs.
With less profit machines will switch off and regular home miners would be in with a shot again. Then it'll reverse again. It's a very fluid system and I don't think we've seen it in action for long enough to be able to easily predict it's future, so obviously I'm just guessing
I've been following the exploits of the banks experimenting with this and I've come to the conclusion that they haven't seen what gives btc it's advantage yet. If all they use the blockchain for is shuffling figures between branches it's not going to make enough of a difference to their business to make it a worthwhile adaption to their business models.
What they've got to realise is that what this tech does is make them obsolete. If they want to exist in the future (assuming enough people choose to use blockchain currencies) they'll simply become service providers, key holders, and we've got enough of them in the bitcoin space as it is. Sure, I reckon there's space for that kind of service, but I don't think all of the current banks will be able to compete with the incumbents.