In my small experience it seems like Boxing is a sport not a martial art.
Both are concerned with fighting, but it's apples and oranges. You eat both but you can't have a taste test really. It's not much use to compare baseball versus basketball.
Whether boxing uses some of the same movement principles as IMA is another question. I think they do share a lot of things. The mindset is worlds apart.
One thing they share is using small movements to produce big results.
Another thing is that they both train one's reactions to be very natural and immediate.
-Jess O