Agree with your premise. Some states, like North Dakota, do require the Presidential candidate to name electors, but the vast majority use the political parties to name them, so the candidate can be replaced without too much effort. The names of the candidates on the ballots may be a different story.
Here is a good summary of the various state laws:
Federal Register | U. S. Electoral College
I think that the states noted as "bound to vote for a specific candidate" is a simplification that assumes the candidate on the voter's ballot is available when the electors cast ballots for president.
That is, it says the electors are bound to a candidate (and the natural assumption is that this is the same as the candidate named on the voter's ballot), but does not give any state deadline for the party to change its candidate. There is a federal deadline, 6 days before the electors cast ballots for president (in December), IIRC.
Of course, there are also deadlines for a presidental candidate to get his or her name on the voter's ballot. But the name so placed is not absolutely binding on the elector or party, particularly if the person so named is unavailable at the time the elector is required to cast his or her ballot.
http://www.ncsl.org/programs/legman/elect/ElectoralCollege.htm <-- Another summary