For example you could plant them in the ground and use them to grow more potatoes or you could chop and fry them into chips, bake and serve them with with chilli etc.
His issue is not really with the cost of software (that is more a side effect of the GPL). He takes issue with the fact that with software you often have artificial restrictions in use and that the manufacturer may include features that are not to your benefit (e.g DRM , spyware , adware) and you can not remove these without breaking the license agreement.
He would liken this more to buying some potatoes that can only be legally used for one purpose and if you wish to use (physically identical) potatoes for another purpose then you must pay a higher fee.
The commercial issue with the GPL is that if you give people the rights to distribute as they see fit there is guarantee that they will give anything back to the original author.
Personally I would love to get applications with source code available that I can modify as I wish (or just fix bugs) but would require that the original author was paid a fee upon re-distribution (of original or modified version) to someone who did not already hold a license. I see this as a very good compromise in many cases.
The problem with this of course is that if I did wish to distribute the software to an unlicensed person then I could easily remove any copy protection methods prior to doing so.
In such a case ironically the best solution might be stronger copyright legislation to protect the rights of open source but non gratis software developers.