I say this as a software developer and one who is not libertarian in the least.
Competent business owners, managers and technical people making decisions about the implementation of software are very interested in the value of that software and its value to business is exactly why we have an economy that exchanges money for these things.
There are some cases where it is possible to limit the supply of digital goods, and this is best seen in software where access to the code can be limited or the code can be written to be restricted in some way, especially in compiled software or web applications. But this, too, can often be hacked.
Note, I'm no fan of free markets. I think they are an enormously clumsy tool for linking 'price' to 'value'.
Wouldn't books, then, only be "worth" the cost of the paper on which they're printed? How does making something digital automatically destroy any inherent value?
But look at it this way, for anything digital the supply is infinite. We currently have legal methods of restricting the supply and some attempts at software or digital methods of restricting it. But even so, the difficulty we've had stamping out illegal piracy is a testament to how artificial and fragile these methods are. With truly infinite supply, the price will always be zero. Why should I pay for something I can create copies of with 'cntrl+c' and 'cntrl+v' ? The only thing that leads me to pay for basically anything is that I can't simply recreate it on my own. The day 3D printers reach the versatility of Star Trek replicators is the day a price based market economy will collapse completely. With infinite supply, there's no need to pay for anything.
The only reason price based markets even work for any other sort of exchange is because there is limited supply. With anything digital the supply is inherently unlimited.