list assignment

[Norvell Spearman]

In "Learning Python," by Lutz and Ascher, there's a table showing different 
assignment statement forms.  One form shown is list assignment.  The authors 
give this as an example:

     [spam, ham] = ['yum', 'YUM']

I don't see how this is any different than a tuple unpacking assignment:

     >>> a, b = 1, 2
     >>> a, b
     (1, 2)
     >>> [a, b] = [1, 2]
     >>> a, b
     (1, 2)

In both instances the names a and b are both mapped to 1 and 2 so why are there 
two different forms?

Thanks for any answers.

--
Norvell Spearman