I think the idea that the government can regulate everything and enforce its laws is becoming a little dated. Think of media piracy or Edward Snowden, for example. The digital domain has made a lot of things possible that were unthinkable 20 years ago. I'm not saying that's a good thing. I just think we've entered an era that is a lot more chaotic. It borders on anarchy.
I think you're right, we're entering a very different era, especially when it comes to the digital actions of individuals.
I think the government might have an easier time regulating bitcoin than piracy because federal and state governments have much more regulatory visibility and control over commerce than they do over individuals and their internet connections (for now). I think the U.S. government is more interested in taxing bitcoin at the moment than eradicating it, but if that changed, all the government would need to do to take a big bite out of bitcoin would be to place the restrictions on businesses and financial institutions that make it illegal to accept bitcoins. With music piracy, there are many more actors, who are much more anonymous. It's much, much easier for the government to make life hard for a few commercial actors than for a large number of individuals. Commercial enterprises have "hooks" by which the government can grab them: business licenses, and in the case of larger companies, public disclosures of assets, etc. They're a lot easier to reach. And, if such regulation were put in place, a currency that businesses couldn't legally accept would not be worth much.
But we're not there yet (and may never get there), and I think that's probably for the best; I'm dispositionally in favor of innovation, even in something as prosaic as currency. So far most of the U.S. actors who might be in a position to regulate it seem to find it more interesting than threatening:
http://www.forbes.com/sites/kashmirhill/2013/11/07/federal-reserve-economist-on-bitcoin-small-phenomenon-but-growing/ . Although there have been some troubling developments recently:
http://www.forbes.com/sites/kashmirhill/2013/08/12/every-important-person-in-bitcoin-just-got-subpoenaed-by-new-yorks-financial-regulator/I think the bigger real risk is market panics in response to milder government intervention: because the value of Bitcoins is consensus based, when governments try to get involved, the markets panic and bitcoin values plunge (check out the article jmone posted above).