In Bill Wasik’s talk about modern media, he discusses how "shorter content will always be free". This is a rather generalizing statement, that is only made true when applying specific parameters to it. A more true statement would be "Short and non-unique content that lacks scarcity will always be free."
The "non-unique" component is necessary, otherwise iTunes immediately proves the statement false. Nearly all of songs on the iTunes music store could be considered relatively "short". However, if the standard song isn't considered to be short enough, there also exists a massive economy in the "ringtone industry" (which are generally 10-15 seconds in length). In other media, iTunes also sells several film shorts in there online store, some of which are quite successful. In the space of "unique" content, people are not paying for quantity, but rather an auditory or visual experience.
The "lack of scarcity" component greater covers content as information, rather than something experiential (like music or film). As Wasik pointed out himself, "short is inherently free because there is so much of it." For example, as long as there are thousands of individuals willing to share free videos of dancing kittens, the "Cat Dancing Video Industry" will never be able to monetize themselves. The same holds true with news. There is such an abundance of free news information, that it is silly for a consumer to pay for it. However, length ("shorter") does not play into the free aspect here either. There are plenty of services online that sell "Sports Handicapping" information at a premium. The length of this information sold is quite minimal, but because there is a scarcity of "expert" opinion, people are willing to pay for this content.
I think Wasik made the comment of "shorter content will always be free" as a way of degrading "free", for the sole purpose of emphasizing his point that we greater value the things we buy. With the surplus of content available online, it's easy to consume it all will very little impact. However, if we make some sort of personal investment into our consumptions, we are more likely to appreciate them.