So the question remains on the 'first sale' right while comparing what you can do with a physical CD to a dematerialized song:
The consensus among Reg readers is that the purchasing a physical medium is not the same as buying a download. In the first case you're buying the physical disc, in the second, you're actually buying the song, so the US' 'first sale' right doesn't apply.
We think the point's still moot, however. If 'first sale' rights are granted when you by a CD, because you're actually buying the disc not the song, you could argue that the same applies to a file. A file can be defined as a data carrier as much as a disc, particularly when it's essentially an authorised copy of a 'master' file.
With music going purely digital through electronic sale delivery, this question is legitimate.