Moreover, one of the arguments outlines "[the NC clauses] are unlikely to increase the potential profit from your work". I think this is true (I could have said, 'I believe this is true', but that would only introduce unqualified trust): the material already being free to some extend, the material will itself is not-profitable, but the services around would be. But, by making it impossible to allow other to set up 'services' around the material (education at a high-fee university, books, software you sell on CD, a webservice for which you require fees for high-volume use, ... remember, 'commercial' is not well-defined), you also make it impossible to build a community around the material; and as such, you reduce the value of the material, also for yourself. FaceBook would not be what it is right now, without community building (neither would the CDK).
These issues are acknowledged by Creative Commons themselves too, and they wrote up an interesting report last year about how commercial use is understood. The bottom line is that no one really knows. I guess. I have not fully read the report yet, but anticipate it is a must read. Here is a bit of the executive summary as a teaser:
- The most notable differences among subgroups within each sample of creators and users are between creators who make money from their works, and those who do not, and between users who make money from their uses of others’ works, and those who do not. In both cases, those who make money generally rate the uses studied less commercial than those who do not make money. The one exception is, again, with respect to personal or private uses by individuals: users who make money consider these uses more commercial than those who do not make money.