On the other hand, if someone goes out and properly buys some music,
> regardless of the medium (78 or iPod), they ought to have some
> reasonably usage on multiple players, just as they do with computer
> software. If I buy a computer program, I can put it on as many
> machines as I want (home, office, car, etc.) as long as it's single > usage.
No.
Leaving aside for the moment the various permutations of "buy", the owners of the copyright of the computer program may and frequently do claim that your use of it is constrained by conditions they supply in the package; such conditions may or may not -- indeed I believe the latter to be more often the case -- permit such uses as you claim.
So, if I buy some music, I should be allowed to freely
> duplicate it as I see fit for my tape player, for example.
Again, ignoring the discussion of what "buy" means, no.
The willingness of the copyright owners to allow you to use their product can be subject to conditions which they can set. These conditions may be further modified by legislation. You can choose to "buy" this music and limit (or not, at you peril) your use to the conditions, or to not "buy" that music and to "buy" other music with different conditions.