IMO, the iterators are introduced at the correct point.  

There are many topics that one could argue should be introduced early, but of course they can't all go earlier (classes should be introduced earlier because everything in python is an object; namespaces should be introduced earlier because they are core concept that affects everything from function locals, to closures, classes, instances, and modules).

I concur with Jim that dropping more terminology earlier in the tutorial doesn't serve the user well.