Is mapping journalism? I would say yes.
Although mapping is always used as a tool or just inserted in the news reports as a supplement, I consider it to be journalism. I think it does the same as what infographics and charticles do.
This is a good example telling disparities in popular vote versus seats won by state in 2012, and did a compare with that in 2010. Explaining this by mapping, I think, is more visual than telling it in long articles or by simply listing numbers.
Also, here is an example of how mapping can tell more than traditional news reports do. I think mapping is a good way to tell stories in new media era. It does not require a big space, yet can give a lot of information.
One thing I found interesting: in this case, Mark Newman draw a series of maps to show 2012 U.S. presidential election results. It shows that if you use different measures when making the map (by population cartogram or by state or by county, etc), you will get the maps slightly different. So how to keep the accuracy of mapping in journalism might be what journalists need to concern about.