The interesting thing with Adobe products is that they have both features that are most useful to a professional (e.g. CMYK) but also features that are really useful to rank amateurs (e.g graphic styles, context-aware fill). I recommend that everyone start with a free tool and see how you like it. Then look at the feature set of a commercial tool, whether it be Adobe, Xara, or Sai and decide if those features would help you out.
The documents that I put together for my campaign could certainly be put together with Inkscape. However, Illustrator has some features that make it easier for me to put together. I wouldn't want to spend the money on Illustrator until I'd evaluated Inkscape and decided that the feature differences really would save me time and make it worth it.
In my mind its similar to a question of why use a pen, when you can paint with a brush. Vector apps like Xara, Illustrator, Inkscape work like using a pen - hard lines, defined shapes based on lines. Painting is a completely different animal. You need to perform tricks to get a brush to draw a hardline. A painting is nothing like a hand drawing - they are two very different styles. So the argument of whether to use a vector application versus an image editor has nothing to do with the qualities or tools in each program. In general the two create very different things - different styles. Some of us like to draw. Some of us like to paint (some like to do both.) I think of vector like drawing, and think image editor like painting. Truth is, I hate to paint, but I like the results of a good painting. So I accomplish both with the drawing tool, as it works best for me.
Really that's what your choice of software is all about - what works best for you. There is no one universal program to best create a map with - it is only dependant on what works best in your hands. Software is just a tool. We, the cartographers, are the artists - choose the artist's tool that works best for you.
PS: lots of software other than Adobe has CMYK functions built in - Xara does and it costs a fraction of what any Adobe program does. Don't let yourself be confused in thinking Adobe is for pros and others are not. I'm a pro and I hardly ever use Adobe products, in fact I create finished work in Xara, work in or export to CMYK (if needed) with final work ready for commercial printing or whatever the end-step is supposed to be. Saying Adobe is for professional work has little weight at all.