Pickling, for one.

  >>> nt = namedtuple('nt', 'a b')
  >>> nt10k = [nt(1, 2) for i in range(10000)]
  >>> dict10k = [{'a':1, 'b':2} for i in range(10000)]
  >>> timeit pickle.dumps(nt10k)
  10 loops, best of 3: 26.3 ms per loop
  >>> timeit pickle.dumps(dict10k)
  100 loops, best of 3: 2.49 ms per loop

If you look at the the StackOverflow in my sibling comment to yours, running 'obj.attrname' on a namedtuple takes longer because it needs to translate 'attrname' to an integer index and then run (e.g.) 'obj[0]'. Outside of that, I'm not sure.