(Insert standard IANAL preface here. What follows are my own non-professional thoughts on the matter)
The petition is utilizing the observation that there are certain rights associated with the terminology of "buying" (or "selling") some product that have been developed over hundreds of years with laws regarding physical commodities. Physical objects are relatively simple to understand; the right to resell or repurpose a physical object is well understood, for example. Such rights are not merely an artifact of the legal system but are inherent to the nature of physical things. No matter the letter of the law, the purchase of a physical object implicates its transfer of possession and the physical capabilities such possession implies (destruction, use, retooling, repurposing, reselling, etc).
Intellectual constructs are a different matter, be it the selling of such intellectual consctructs that interface with physical commodities --think healthcare or perhaps selling access to some physical but expensive machine-- or the selling of intellectual constructs themselves --like stories or other expressions of ideas. The law has frustratingly used traditional property laws as its basis for investigating rights and liabilities with respect to these intellectual constructs, despite mounting observations that such a foundation is typically unsound. Licenses for software, as an example, can arbitrarily grant and deny rights, unlike the rights of physical commodities that are an inherent consequence of their physical nature.
The practical consequence for a consumer is that the "buying" that occurs for a license or some other intellectual construct has the potential to bear _little_ resemblance or _significant_ resemblance to the traditional notions of "buying" a physical commodity that consumers have been exposed to for centuries. The rights associated with various software licenses, for instance, can vary considerably. "Buying" a piece of GPL software and "buying" a piece of DRM-restricted and/or proprietary software are not, by any reasonable interpretation of each situation, the same thing. One who purchases a GPL-licensed piece of software is closer to the spirit of the term "buy" in its historical context of the transfer of physical commodities at some set price. Purchasing the proprietary and DRM'd software is more akin to "licensing" its use for specific cases and more closely aligns with contract law vis a vis services rendered.
Perhaps it would be better to say that one never "buys" software outright but rather "purchases a license," the rights and liabilities of which may vary dramatically, thus sidestepping the historical connotations of "buying" a physical object. But then of course the consumer loses any and all distinction between different types of licenses, effectively introducing the same problem as attempting to use only the term "buying." In such a case, rights that were once well-understood and reasonably presupposed by the consumer are now entirely up in the air and largely in the hands of the producer. In either case, it's clear to me that conflating the terms introduces problems.
I believe the presence of restrictive DRM could serve as a useful litmus test in gauging where on the scale such "licenses" to intellectual constructs fall and thus whether the term "buy" or "license" would be more appropriate. The current example on the crest of the news deals with the SimCity games. I know I would say that I "bought" SimCity 2000 (regardless of what the letter of the law would implicate). However, if I were to fork over cash for the most recent version of the SimCity franchise, I would never say that I "bought" it, but rather that I "licensed" it.