Yes, that’s true, but the legal and economic constraints to copying digital goods still exist. People still need to make money to pay their bills. So, the economic incentive to sell digital goods is quite high.
For an optimally working economy, digital goods should be copied and shared freely. Selling services and material goods makes perfect sense, but selling digital goods only creates artificial scarcity, because you first have to withhold something from the public before you can sell it.
In the digital realm we can have nearly limitless abundance! What can be digitized, can in theory be copied to everyone. Disk space and bandwidth are the only remaining limitations. That we don’t use this potential abundance fully is a serious flaw of our current economic paradigm. That is what motivated the creation of the Pirate Parties. And what motivated me to create my reputation economy system Quantified Prestige. If a sufficient number of people adopt that system, then the economics of digital goods would make sense: People produce digital goods, consumers use them, reward the producers with reputation. Reputation translates into an income in a flux currency. Flux currencies are traded for services or material goods. Artists and coders don’t need to starve, and everyone is happy. 
It gets even better when we have this state of digital abundance: A lot of the value of current goods lie in their information. But if information becomes free, most goods will become significantly cheaper. Also, 3d printing technologies are getting better at an astonishing rate. In the future, we will be able to copy blueprints for all kinds of goods and simply print them out. We will only need to pay for the cheap printing materials.
Of course, we will also be able to print the fanciest houses. 3d printing houses is already possible today. And the price of doing that will go down and down. It might be worth considering how cheap it would be to print a community house with the best and cheapest technological methods available today.
But let’s come back to advertisement in real life again. I wonder why there isn’t more advertisement already. For example, people could be wearing clothes that have lots of ads on them. They wouldn’t pay for the clothes – instead they would be paid for wearing them! Advertisement on cars is another underutilized possibility. Or advertisement on the outside of regular houses. It seems that these possible “capitalist” ideas don’t seem to catch on. Why? Are people not desperate enough to finance their lifestyle through advertisements? Why do so many people opt for free ad-financed apps then?
Why don’t government draw advertisements on roads (sure, they will be eroded relatively quickly, but that would be quite fitting for short-lived “trendy” products)?
Why don’t we get internet, landlines, and mobile connections for free for getting advertisement calls at irregular intervals?
There seem to be cultural barriers against the ubiquitous adoption of advertisement sponsored products. Do they even make sense?